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‎README.md

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@@ -27,6 +27,7 @@ Your ideas/fixes/algorithms are more than welcome!
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|678|[Valid Parenthesis String](https://leetcode.com/problems/valid-parenthesis-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_678.java) | O(n) | O(1) | Medium| Recursion, Greedy
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|677|[Map Sum Pairs](https://leetcode.com/problems/map-sum-pairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_677.java) | O(n) | O(n) | Medium | HashMap
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|676|[Implement Magic Dictionary](https://leetcode.com/problems/implement-magic-dictionary/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_676.java) | O(n^2) | O(n) | Medium |
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|675|[Cut Off Trees for Golf Event](https://leetcode.com/problems/cut-off-trees-for-golf-event/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_675.java) | O((m*n)^2) | O(m*n) | Hard | BFS
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|674|[Longest Continuous Increasing Subsequence](https://leetcode.com/problems/longest-continuous-increasing-subsequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_674.java) | O(n^2) | O(1) | Easy |
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|672|[Bulb Switcher II](https://leetcode.com/problems/bulb-switcher-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_672.java) | O(1) | O(1) | Medium | Math
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|671|[Second Minimum Node In a Binary Tree](https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_671.java) | O(n) | O(n) | Easy | Tree, DFS

‎src/main/java/com/fishercoder/solutions/_675.java

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package com.fishercoder.solutions;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.PriorityQueue;
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import java.util.Queue;
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/**
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* 675. Cut Off Trees for Golf Event
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*
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* You are asked to cut off trees in a forest for a golf event.
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* The forest is represented as a non-negative 2D map, in this map:
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* 0 represents the obstacle can't be reached.
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* 1 represents the ground can be walked through.
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*
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* The place with number bigger than 1 represents a tree can be walked through,
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* and this positive number represents the tree's height.
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*
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* You are asked to cut off all the trees in this forest in the order of tree's height -
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* always cut off the tree with lowest height first.
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* And after cutting, the original place has the tree will become a grass (value 1).
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*
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* You will start from the point (0, 0) and you should output the minimum steps you need to walk to cut off all the trees.
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*
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* If you can't cut off all the trees, output -1 in that situation.
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* You are guaranteed that no two trees have the same height and there is at least one tree needs to be cut off.
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*
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* Example 1:
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* Input:
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* [
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* [1,2,3],
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* [0,0,4],
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* [7,6,5]
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* ]
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* Output: 6
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*
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* Example 2:
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* Input:
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* [
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* [1,2,3],
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* [0,0,0],
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* [7,6,5]
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* ]
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* Output: -1
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*
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* Example 3:
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* Input:
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* [
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* [2,3,4],
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* [0,0,5],
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* [8,7,6]
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* ]
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* Output: 6
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*
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* Explanation: You started from the point (0,0) and you can cut off the tree in (0,0) directly without walking.
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* Hint: size of the given matrix will not exceed 50x50.
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*/
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public class _675 {
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public static class Solution1 {
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public int cutOffTree(List<List<Integer>> forest) {
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if (forest == null || forest.isEmpty() || forest.size() == 0 || forest.get(0).get(0) == 0) {
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return -1;
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}
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int m = forest.size();
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int n = forest.get(0).size();
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/**cut trees in ascending order*/
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PriorityQueue<Tree> heap = new PriorityQueue<>((a, b) -> a.height - b.height);
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for (int i = 0; i < m; i++) {
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for (int j = 0; j < n; j++) {
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if (forest.get(i).get(j) > 1) {
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/**This is important: we'll add trees that are only taller than 1!!!*/
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heap.offer(new Tree(i, j, forest.get(i).get(j)));
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}
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}
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}
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int sum = 0;
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Tree start = new Tree();
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while (!heap.isEmpty()) {
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Tree curr = heap.poll();
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int step = bfs(forest, curr, start, m, n);
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if (step == -1) {
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return -1;
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}
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sum += step;
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start = curr;
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}
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return sum;
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}
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private int bfs(List<List<Integer>> forest, Tree target, Tree start, int m, int n) {
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int[] dirs = new int[]{0, 1, 0, -1, 0};
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boolean[][] visited = new boolean[m][n];
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Queue<Tree> queue = new LinkedList<>();
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queue.offer(start);
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visited[start.x][start.y] = true;
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int step = 0;
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while (!queue.isEmpty()) {
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int size = queue.size();
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for (int k = 0; k < size; k++) {
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Tree tree = queue.poll();
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if (tree.x == target.x && tree.y == target.y) {
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return step;
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}
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for (int i = 0; i < 4; i++) {
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int nextX = tree.x + dirs[i];
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int nextY = tree.y + dirs[i + 1];
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if (nextX < 0 || nextY < 0 || nextX >= m || nextY >= n || visited[nextX][nextY] || forest.get(nextX).get(nextY) == 0) {
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continue;
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}
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queue.offer(new Tree(nextX, nextY, forest.get(nextX).get(nextY)));
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visited[nextX][nextY] = true;
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}
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}
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step++;
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}
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return -1;
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}
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class Tree {
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int x;
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int y;
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int height;
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public Tree(int x, int y, int height) {
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this.x = x;
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this.y = y;
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this.height = height;
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}
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public Tree() {
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this.x = 0;
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this.y = 0;
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this.height = 0;
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}
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}
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}
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}

‎src/test/java/com/fishercoder/_675Test.java

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package com.fishercoder;
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import com.fishercoder.common.utils.ArrayUtils;
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import com.fishercoder.solutions._675;
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import org.junit.BeforeClass;
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import org.junit.Test;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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import static org.junit.Assert.assertEquals;
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public class _675Test {
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private static _675.Solution1 solution1;
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private static List<List<Integer>> forest;
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@BeforeClass
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public static void setup() {
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solution1 = new _675.Solution1();
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}
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@Test
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public void test1() {
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forest = new ArrayList<>();
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forest.add(Arrays.asList(1, 2, 3));
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forest.add(Arrays.asList(0, 0, 4));
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forest.add(Arrays.asList(7, 6, 5));
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assertEquals(6, solution1.cutOffTree(forest));
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}
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@Test
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public void test2() {
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forest = new ArrayList<>();
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forest.add(Arrays.asList(1, 2, 3));
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forest.add(Arrays.asList(0, 0, 0));
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forest.add(Arrays.asList(7, 6, 5));
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assertEquals(-1, solution1.cutOffTree(forest));
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}
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@Test
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public void test3() {
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forest = new ArrayList<>();
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forest.add(Arrays.asList(2, 3, 4));
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forest.add(Arrays.asList(0, 0, 5));
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forest.add(Arrays.asList(8, 7, 6));
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assertEquals(6, solution1.cutOffTree(forest));
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}
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@Test
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public void test4() {
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forest = ArrayUtils.buildList(new int[][]{
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{2, 3, 4, 9},
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{0, 0, 5, 10},
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{8, 7, 6, 12},
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});
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assertEquals(13, solution1.cutOffTree(forest));
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}
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@Test
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public void test5() {
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forest = ArrayUtils.buildList(new int[][]{
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{0, 0, 0, 3528, 2256, 9394, 3153},
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{8740, 1758, 6319, 3400, 4502, 7475, 6812},
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{0, 0, 3079, 6312, 0, 0, 0},
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{6828, 0, 0, 0, 0, 0, 8145},
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{6964, 4631, 0, 0, 0, 4811, 0},
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{0, 0, 0, 0, 9734, 4696, 4246},
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{3413, 8887, 0, 4766, 0, 0, 0},
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{7739, 0, 0, 2920, 0, 5321, 2250},
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{3032, 0, 3015, 0, 3269, 8582, 0}});
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assertEquals(-1, solution1.cutOffTree(forest));
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}
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@Test
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public void test6() {
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forest = ArrayUtils.buildList(new int[][]{
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{54581641, 64080174, 24346381, 69107959},
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{86374198, 61363882, 68783324, 79706116},
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{668150, 92178815, 89819108, 94701471},
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{83920491, 22724204, 46281641, 47531096},
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{89078499, 18904913, 25462145, 60813308}
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});
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assertEquals(57, solution1.cutOffTree(forest));
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}
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}

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