add cpp solution

Author: jinshendan

May-LeetCoding-Challenge/26-Contiguous-Array/Contiguous-Array.cpp

@@ -0,0 +1,19 @@
+class Solution {
+public:
+    int findMaxLength(vector<int>& nums) {
+        int n = nums.size();
+        int sum = 0;
+        map<int, int> min_index;
+        
+        int ans = 0;
+        for (int i = 0; i < n; i++){
+            sum += (nums[i] == 0)?-1:1;
+            if (sum == 0) ans = i+1;
+            else if (min_index.find(sum) == min_index.end())
+                min_index[sum] = i;
+            else ans = max(ans, i - min_index[sum]);
+        }
+        return ans;
+    }
+};
+