New Problem Solution "Integer Replacement"

Author: haoel

README.md

@@ -8,6 +8,7 @@ LeetCode
 
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
+|397|[Integer Replacement](https://leetcode.com/problems/integer-replacement/) | [C++](./algorithms/cpp/integerReplacement/IntegerReplacement.cpp)|Medium|
 |396|[Rotate Function](https://leetcode.com/problems/rotate-function/) | [C++](./algorithms/cpp/rotateFunction/RotateFunction.cpp)|Easy|
 |395|[Longest Substring with At Least K Repeating Characters](https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters/) | [C++](./algorithms/cpp/longestSubstringWithAtLeastKRepeatingCharacters/LongestSubstringWithAtLeastKRepeatingCharacters.cpp)|Medium|
 |394|[Decode String](https://leetcode.com/problems/decode-string/) | [C++](./algorithms/cpp/decodeString/DecodeString.cpp)|Medium|

algorithms/cpp/integerReplacement/IntegerReplacement.cpp

@@ -0,0 +1,69 @@
+// Source : https://leetcode.com/problems/integer-replacement/
+// Author : Hao Chen
+// Date   : 2016-11-04
+
+/*************************************************************************************** 
+ *
+ * Given a positive integer n and you can do operations as follow:
+ * 
+ * If n is even, replace n with n/2.
+ * If n is odd, you can replace n with either n + 1 or n - 1.
+ * 
+ * What is the minimum number of replacements needed for n to become 1?
+ * 
+ * Example 1:
+ * 
+ * Input:
+ * 8
+ * 
+ * Output:
+ * 3
+ * 
+ * Explanation:
+ * 8 -> 4 -> 2 -> 1
+ * 
+ * Example 2:
+ * 
+ * Input:
+ * 7
+ * 
+ * Output:
+ * 4
+ * 
+ * Explanation:
+ * 7 -> 8 -> 4 -> 2 -> 1
+ * or
+ * 7 -> 6 -> 3 -> 2 -> 1
+ ***************************************************************************************/
+
+class Solution {
+public:
+
+
+    int integerReplacement_recursion(int n) {
+        if ( n <= 1) return 0; // recursive exited point
+        if ( n == INT_MAX ) return 32; // special case to avoid integer overflow.
+        if ( n % 2 == 0 ) return integerReplacement(n/2) + 1;
+        return min( integerReplacement(n+1), integerReplacement(n-1) ) + 1;
+    }
+    
+    int integerReplacement_recursionWithCache(int n) {
+        static unordered_map<int, int> cache;
+        //if hitted the cache, just return the result
+        if (cache.find(n) != cache.end()) return cache[n];
+        
+        int result;
+        if ( n <= 1) return 0; // recursive exited point
+        if ( n == INT_MAX ) return 32; // special case to avoid integer overflow.
+        if ( n % 2 == 0 ) result = integerReplacement(n/2) + 1;
+        else result = min( integerReplacement(n+1), integerReplacement(n-1) ) + 1;
+        
+        //add into cache
+        cache[n] = result;
+        return result;
+    }
+    
+    int integerReplacement(int n) {
+        return integerReplacement_recursionWithCache(n);
+    }
+};