[LEET-541] add 541

fishercoder1534 · fishercoder1534 · commit 1ae0ee11f090 · 2017-03-12T09:10:14.000-07:00
diff --git a/leetcode-algorithms/README.md b/leetcode-algorithms/README.md
@@ -3,6 +3,7 @@
 ## Algorithms
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
+|541|[Reverse String II](https://leetcode.com/problems/reverse-string-ii/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/ReverseStringII.java) | O(n) |O(1) | Easy | String
 |540|[Single Element in a Sorted Array](https://leetcode.com/problems/single-element-in-a-sorted-array/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SingleElementinaSortedArray.java) | O(n) |O(1) | Medium | 
 |535|[Encode and Decode TinyURL](https://leetcode.com/problems/encode-and-decode-tinyurl/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/EncodeandDecodeTinyURL.java) | O(1) |O(n) | Medium | Design
 |532|[K-diff Pairs in an Array](https://leetcode.com/problems/k-diff-pairs-in-an-array/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/KdiffPairsinanArray.java) | O(n) |O(n) | Easy | HashMap
diff --git a/leetcode-algorithms/src/main/java/com/stevesun/solutions/ReverseStringII.java b/leetcode-algorithms/src/main/java/com/stevesun/solutions/ReverseStringII.java
@@ -0,0 +1,32 @@
+package com.stevesun.solutions;
+
+/**
+ * Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string.
+ * If there are less than k characters left, reverse all of them.
+ * If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.
+
+ Example:
+ Input: s = "abcdefg", k = 2
+ Output: "bacdfeg"
+
+ Restrictions:
+ The string consists of lower English letters only.
+ Length of the given string and k will in the range [1, 10000]
+ */
+public class ReverseStringII {
+
+    public String reverseStr(String s, int k) {
+        StringBuilder stringBuilder = new StringBuilder();
+        for (int i = 0; i < s.length(); i = i + 2 * k) {
+            if (s.length() >= (i + k)) stringBuilder.append(new StringBuilder(s.substring(i, i + k)).reverse());
+            else {
+                stringBuilder.append(new StringBuilder(s.substring(i)).reverse());
+                break;
+            }
+            if ((i + 2 * k) <= s.length()) stringBuilder.append(s.substring(i + k, i + 2 * k));
+            else stringBuilder.append(s.substring(i + k));
+        }
+        return stringBuilder.toString();
+    }
+
+}
diff --git a/leetcode-algorithms/src/test/java/com/stevesun/ReverseStringIITest.java b/leetcode-algorithms/src/test/java/com/stevesun/ReverseStringIITest.java
@@ -0,0 +1,80 @@
+package com.stevesun;
+
+import com.stevesun.solutions.ReverseStringII;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+public class ReverseStringIITest {
+    private static ReverseStringII test;
+    private static String expected;
+    private static String actual;
+    private static String s;
+    private static int k;
+
+    @BeforeClass
+    public static void setup(){
+        test = new ReverseStringII();
+    }
+
+    @Before
+    public void setupForEachTest(){}
+
+    @Test
+    public void test1(){
+        s = "abcd";
+        k = 5;
+        expected = "dcba";
+        actual = test.reverseStr(s, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test2(){
+        s = "abcdefg";
+        k = 2;
+        expected = "bacdfeg";
+        actual = test.reverseStr(s, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test3(){
+        s = "abcd";
+        k = 4;
+        expected = "dcba";
+        actual = test.reverseStr(s, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test4(){
+        s = "abcdefg";
+        k = 3;
+        expected = "cbadefg";
+        actual = test.reverseStr(s, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test5(){
+        s = "abcd";
+        k = 3;
+        expected = "cbad";
+        actual = test.reverseStr(s, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test6(){
+        s = "hyzqyljrnigxvdtneasepfahmtyhlohwxmkqcdfehybknvdmfrfvtbsovjbdhevlfxpdaovjgunjqlimjkfnqcqnajmebeddqsgl";
+        System.out.println("s.length() = " + s.length());
+        k = 39;
+        expected = "fdcqkmxwholhytmhafpesaentdvxginrjlyqzyhehybknvdmfrfvtbsovjbdhevlfxpdaovjgunjqllgsqddebemjanqcqnfkjmi";
+        actual = test.reverseStr(s, k);
+        assertEquals(expected, actual);
+    }
+
+}
