add 670

Author: fishercoder1534

README.md

@@ -23,6 +23,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
 |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
+|670|[Maximum Swap](https://leetcode.com/problems/maximum-swap/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_670.java) | O(n^2) | O(1) | Medium | String
 |669|[Trim a Binary Search Tree](https://leetcode.com/problems/trim-a-binary-search-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_669.java) | O(n) | O(1) | Easy | Tree, DFS
 |668|[Kth Smallest Number in Multiplication Table](https://leetcode.com/problems/kth-smallest-number-in-multiplication-table/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_668.java) | O(logm*n) | O(1) | Hard | Binary Search
 |667|[Beautiful Arrangement II](https://leetcode.com/problems/beautiful-arrangement-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_667.java) | O(n) | O(1) | Medium | Array

src/main/java/com/fishercoder/solutions/_670.java

@@ -0,0 +1,41 @@
+package com.fishercoder.solutions;
+
+/**
+ * 670. Maximum Swap
+ *
+ * Given a non-negative integer, you could swap two digits at most once to get the maximum valued number.
+ * Return the maximum valued number you could get.
+
+ Example 1:
+ Input: 2736
+ Output: 7236
+ Explanation: Swap the number 2 and the number 7.
+
+ Example 2:
+ Input: 9973
+ Output: 9973
+ Explanation: No swap.
+
+ Note:
+ The given number is in the range [0, 108]
+
+ */
+public class _670 {
+    public static class Solution1 {
+        public int maximumSwap(int num) {
+            String numStr = String.valueOf(num);
+            int max = num;
+            for (int i = 0; i < numStr.length()-1; i++) {
+                for (int j = i+1; j < numStr.length(); j++) {
+                    if (numStr.charAt(i) < numStr.charAt(j)) {
+                        StringBuilder sb = new StringBuilder(numStr);
+                        sb.replace(i, i+1, String.valueOf(numStr.charAt(j)));
+                        sb.replace(j, j+1, String.valueOf(numStr.charAt(i)));
+                        max = Math.max(max, Integer.parseInt(sb.toString()));
+                    }
+                }
+            }
+            return max;
+        }
+    }
+}

src/test/java/com/fishercoder/_670Test.java

@@ -0,0 +1,37 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._670;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _670Test {
+    private static _670.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _670.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(7236, solution1.maximumSwap(2736));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(9973, solution1.maximumSwap(9973));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(73236, solution1.maximumSwap(23736));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(98213, solution1.maximumSwap(91283));
+    }
+
+}