add 1676

fishercoder1534 · fishercoder1534 · commit 00c8d38fcd48 · 2021-07-29T16:14:13.000-07:00
diff --git a/README.md b/README.md
@@ -115,6 +115,7 @@ _If you like this project, please leave me a star._ &#9733;
 |1680|[Concatenation of Consecutive Binary Numbers](https://leetcode.com/problems/concatenation-of-consecutive-binary-numbers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1680.java) ||Medium|Math|
 |1679|[Max Number of K-Sum Pairs](https://leetcode.com/problems/max-number-of-k-sum-pairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1679.java) ||Medium|HashTable|
 |1678|[Goal Parser Interpretation](https://leetcode.com/problems/goal-parser-interpretation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1678.java) ||Easy|String|
+|1676|[Lowest Common Ancestor of a Binary Tree IV](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree-iv/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1676.java) ||Medium|Tree, DFS, Binary Tree|
 |1675|[Minimize Deviation in Array](https://leetcode.com/problems/minimize-deviation-in-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1675.java) ||Hard|Heap, Ordered Map|
 |1673|[Find the Most Competitive Subsequence](https://leetcode.com/problems/find-the-most-competitive-subsequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1673.java) |[:tv:](https://youtu.be/GBJFxSD3B_s)|Medium|Stack, Greedy|
 |1672|[Richest Customer Wealth](https://leetcode.com/problems/richest-customer-wealth/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1672.java) ||Easy|Array|
diff --git a/src/main/java/com/fishercoder/solutions/_1676.java b/src/main/java/com/fishercoder/solutions/_1676.java
@@ -0,0 +1,40 @@
+package com.fishercoder.solutions;
+
+import com.fishercoder.common.classes.TreeNode;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class _1676 {
+    public static class Solution1 {
+        /**
+         * Since there are conditions for this problem: all values in the tree and given nodes are unique, we could simply use a HashSet to track the number of nodes we've found so far during the traversal.
+         */
+        TreeNode lca;
+
+        public TreeNode lowestCommonAncestor(TreeNode root, TreeNode[] nodes) {
+            Set<Integer> target = new HashSet<>();
+            for (TreeNode node : nodes) {
+                target.add(node.val);
+            }
+            dfs(root, target);
+            return lca;
+        }
+
+        private int dfs(TreeNode root, Set<Integer> target) {
+            if (root == null) {
+                return 0;
+            }
+            int leftCount = dfs(root.left, target);
+            int rightCount = dfs(root.right, target);
+            int foundCount = leftCount + rightCount;
+            if (target.contains(root.val)) {
+                foundCount++;
+            }
+            if (foundCount == target.size() && lca == null) {
+                lca = root;
+            }
+            return foundCount;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1676Test.java b/src/test/java/com/fishercoder/_1676Test.java
@@ -0,0 +1,26 @@
+package com.fishercoder;
+
+import com.fishercoder.common.classes.TreeNode;
+import com.fishercoder.common.utils.TreeUtils;
+import com.fishercoder.solutions._1676;
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1676Test {
+    private static _1676.Solution1 solution1;
+
+    @Test
+    public void test1() {
+        solution1 = new _1676.Solution1();
+        TreeNode root = TreeUtils.constructBinaryTree(Arrays.asList(3, 5, 1, 6, 2, 0, 8, null, null, 7, 4));
+        TreeNode node1 = TreeUtils.constructBinaryTree(Arrays.asList(4));
+        TreeNode node2 = TreeUtils.constructBinaryTree(Arrays.asList(7));
+        TreeNode[] nodes = new TreeNode[]{node1, node2};
+        TreeNode lca = TreeUtils.constructBinaryTree(Arrays.asList(2, 7, 4));
+        assertEquals(lca, solution1.lowestCommonAncestor(root, nodes));
+    }
+
+}
