feat: solution for 0724

Author: Guardiaans

724.find-pivot-index.cpp

@@ -0,0 +1,30 @@
+/*
+ * @lc app=leetcode id=724 lang=cpp
+ *
+ * [724] Find Pivot Index
+ */
+
+// @lc code=start
+class Solution {
+public:
+    int pivotIndex(vector<int>& nums) {
+        // explain the codes below:
+        int sum = 0; // sum of all numbers before the pivot
+        // sum of all numbers after the pivot
+        for (int i = 0; i < nums.size(); i++) { 
+            sum += nums[i]; 
+        }
+        int left = 0; // sum of all numbers before the pivot
+        for (int i = 0; i < nums.size(); i++) {
+            // if the sum of all numbers before the pivot is equal to the sum of all numbers after the pivot, then the pivot is at index i
+            if (left == sum - left - nums[i]) { 
+                return i;
+            }
+            left += nums[i];
+        }
+        return -1;
+        
+    }
+};
+// @lc code=end
+