Create find-the-middle-index-in-array.cpp

Author: kamyu104

C++/find-the-middle-index-in-array.cpp

@@ -0,0 +1,17 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    int findMiddleIndex(vector<int>& nums) {
+        const int total = accumulate(cbegin(nums), cend(nums), 0);
+        int accu = 0;
+        for (int i = 0; i < size(nums); ++i) {
+            if (accu * 2 == total - nums[i]) {
+                return i;
+            }
+            accu += nums[i];
+        }
+        return -1;
+    }
+};