add 779

fishercoder1534 · fishercoder1534 · commit efe7940c88b2 · 2018-02-04T09:47:30.000-08:00
diff --git a/README.md b/README.md
@@ -22,6 +22,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|---------------|---------------|--------|-------------|-------------
+|779|[K-th Symbol in Grammar](https://leetcode.com/problems/k-th-symbol-in-grammar/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_779.java) | O(logn) | O(1) | |Medium|
 |771|[Jewels and Stones](https://leetcode.com/problems/jewels-and-stones/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_771.java) | O(n) | O(m) | |Easy|
 |767|[Reorganize String](https://leetcode.com/problems/reorganize-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_767.java) | O(klogk) k is the number of unique characters in given String| O(k) | |Medium|
 |766|[Toeplitz Matrix](https://leetcode.com/problems/toeplitz-matrix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_766.java) | O(m*n) | O(1) | |Easy|
diff --git a/src/main/java/com/fishercoder/solutions/_779.java b/src/main/java/com/fishercoder/solutions/_779.java
@@ -0,0 +1,74 @@
+package com.fishercoder.solutions;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * 779. K-th Symbol in Grammar
+ *
+ * On the first row, we write a 0. Now in every subsequent row,
+ * we look at the previous row and replace each occurrence of 0 with 01, and each occurrence of 1 with 10.
+ * Given row N and index K, return the K-th indexed symbol in row N. (The values of K are 1-indexed.) (1 indexed).
+
+ Examples:
+ Input: N = 1, K = 1
+ Output: 0
+
+ Input: N = 2, K = 1
+ Output: 0
+
+ Input: N = 2, K = 2
+ Output: 1
+
+ Input: N = 4, K = 5
+ Output: 1
+
+ Explanation:
+ row 1: 0
+ row 2: 01
+ row 3: 0110
+ row 4: 01101001
+
+ Note:
+
+ N will be an integer in the range [1, 30].
+ K will be an integer in the range [1, 2^(N-1)].
+ */
+
+public class _779 {
+  public static class Solution1 {
+    /**Time: O(2^n)
+     * Space: O(2^n)
+     * This will result int TLE.*/
+    public int kthGrammar(int N, int K) {
+      List<List<Integer>> lists = new ArrayList<>();
+      lists.add(Arrays.asList(0));
+      for (int i = 1; i <= N; i++) {
+        List<Integer> curr = new ArrayList<>();
+        List<Integer> prev = lists.get(i - 1);
+        for (int j = 0; j < prev.size(); j++) {
+          if (prev.get(j) == 0) {
+            curr.add(0);
+            curr.add(1);
+          } else {
+            curr.add(1);
+            curr.add(0);
+          }
+        }
+        lists.add(curr);
+      }
+      return lists.get(N).get(K - 1);
+    }
+  }
+
+  public static class Solution2 {
+    /**Time: O(logn)
+     * Space: O(1)*/
+    public int kthGrammar(int N, int K) {
+      return Integer.bitCount(K - 1) % 2;
+    }
+
+  }
+
+}
diff --git a/src/test/java/com/fishercoder/_779Test.java b/src/test/java/com/fishercoder/_779Test.java
@@ -0,0 +1,42 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._779;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _779Test {
+  private static _779.Solution1 solution1;
+  private static _779.Solution2 solution2;
+
+  @BeforeClass
+  public static void setup() {
+    solution1 = new _779.Solution1();
+    solution2 = new _779.Solution2();
+  }
+
+  @Test
+  public void test1() {
+    assertEquals(0, solution1.kthGrammar(1, 1));
+    assertEquals(0, solution2.kthGrammar(1, 1));
+  }
+
+  @Test
+  public void test2() {
+    assertEquals(0, solution1.kthGrammar(2, 1));
+    assertEquals(0, solution2.kthGrammar(2, 1));
+  }
+
+  @Test
+  public void test3() {
+    assertEquals(1, solution1.kthGrammar(2, 2));
+    assertEquals(1, solution2.kthGrammar(2, 2));
+  }
+
+  @Test
+  public void test4() {
+    assertEquals(1, solution1.kthGrammar(4, 5));
+    assertEquals(1, solution2.kthGrammar(4, 5));
+  }
+}
