add 395

fishercoder1534 · fishercoder1534 · commit 50cf51e4bdd8 · 2017-09-15T08:19:39.000-07:00
diff --git a/README.md b/README.md
@@ -242,6 +242,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |398|[Random Pick Index](https://leetcode.com/problems/random-pick-index/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_398.java) | | | Medium| Reservoir Sampling
 |397|[Integer Replacement](https://leetcode.com/problems/integer-replacement/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_397.java)| ? | ? | Easy| BFS
 |396|[Rotate Function](https://leetcode.com/problems/rotate-function/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_396.java)| O(n^2) could be optimized to O(n) | O(1) | Easy|
+|395|[Longest Substring with At Least K Repeating Characters](https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_395.java)| O(n^2) | O(1) | Medium| Recursion
 |393|[UTF-8 Validation](https://leetcode.com/problems/utf-8-validation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_393.java)| O(?)|O(?) | Medium| Bit Manipulation
 |392|[Is Subsequence](https://leetcode.com/problems/is-subsequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_392.java)| O(m*n)|O(1) | Medium| Array, String
 |391|[Perfect Rectangle](https://leetcode.com/problems/perfect-rectangle/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_391.java)| O(n)|O(1) | Hard| 
diff --git a/src/main/java/com/fishercoder/solutions/_395.java b/src/main/java/com/fishercoder/solutions/_395.java
@@ -0,0 +1,61 @@
+package com.fishercoder.solutions;
+
+/**
+ * 395. Longest Substring with At Least K Repeating Characters
+ *
+ *  Find the length of the longest substring T of a given string
+ *  (consists of lowercase letters only)
+ *  such that every character in T appears no less than k times.
+
+ Example 1:
+ Input:
+ s = "aaabb", k = 3
+
+ Output:
+ 3
+
+ The longest substring is "aaa", as 'a' is repeated 3 times.
+
+
+ Example 2:
+ Input:
+ s = "ababbc", k = 2
+
+ Output:
+ 5
+
+ The longest substring is "ababb", as 'a' is repeated 2 times and 'b' is repeated 3 times.
+ */
+
+public class _395 {
+    public static class Solution1 {
+        /**Reference: https://discuss.leetcode.com/topic/57372/java-divide-and-conquer-recursion-solution*/
+        public int longestSubstring(String s, int k) {
+            return findLongestSubstring(s.toCharArray(), 0, s.length(), k);
+        }
+
+        int findLongestSubstring(char[] chars, int start, int end, int k) {
+            if (end - start < k) {
+                return 0;
+            }
+            int[] count = new int[26];
+            for (int i = start; i < end; i++) {
+                int index = chars[i] - 'a';
+                count[index]++;
+            }
+
+            for (int i = 0; i < 26; i++) {
+                if (count[i] < k && count[i] > 0) {
+                    for (int j = start; j < end; j++) {
+                        if (chars[j] == i + 'a') {
+                            int left = findLongestSubstring(chars, start, j, k);
+                            int right = findLongestSubstring(chars, j + 1, end, k);
+                            return Math.max(left, right);
+                        }
+                    }
+                }
+            }
+            return end - start;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_395Test.java b/src/test/java/com/fishercoder/_395Test.java
@@ -0,0 +1,31 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._395;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+/**
+ * Created by fishercoder on 12/31/16.
+ */
+public class _395Test {
+
+    private static _395.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _395.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(5, solution1.longestSubstring("ababbc", 2));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(3, solution1.longestSubstring("aaabb", 3));
+    }
+
+}
