solve problem Find Pivot Index

Author: P-ppc

README.md

@@ -142,6 +142,7 @@ All solutions will be accepted!
 |141|[Linked List Cycle](https://leetcode-cn.com/problems/linked-list-cycle/description/)|[java/py/js](./algorithms/LinkedListCycle)|Easy|
 |387|[First Unique Character In A String](https://leetcode-cn.com/problems/first-unique-character-in-a-string/description/)|[java/py/js](./algorithms/FirstUniqueCharacterInAString)|Easy|
 |628|[Maximum Product Of Three Numbers](https://leetcode-cn.com/problems/maximum-product-of-three-numbers/description/)|[java/py/js](./algorithms/MaximumProductOfThreeNumbers)|Easy|
+|724|[Find Pivot Index](https://leetcode-cn.com/problems/find-pivot-index/description/)|[java/py/js](./algorithms/FindPivotIndex)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/FindPivotIndex/README.md

@@ -0,0 +1,2 @@
+# Find Pivot Index
+This problem is easy to solve

algorithms/FindPivotIndex/Solution.java

@@ -0,0 +1,18 @@
+class Solution {
+    public int pivotIndex(int[] nums) {
+        int totalSum = 0,
+            leftSum = 0;
+        
+        for (int num : nums) totalSum += num;
+        
+        for (int i = 0; i < nums.length; i++) {
+            if (leftSum == totalSum - nums[i] - leftSum) {
+                return i;
+            } else {
+                leftSum += nums[i];
+            }
+        }
+        
+        return -1;
+    }
+}

algorithms/FindPivotIndex/solution.js

@@ -0,0 +1,20 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var pivotIndex = function(nums) {
+    let totalSum = 0,
+        leftSum = 0
+    
+    nums.forEach(num => totalSum += num)
+    
+    for (let i = 0; i < nums.length; i++) {
+        if (leftSum === totalSum - nums[i] - leftSum) {
+            return i
+        } else {
+            leftSum += nums[i]
+        }
+    }
+    
+    return -1
+};

algorithms/FindPivotIndex/solution.py

@@ -0,0 +1,19 @@
+class Solution(object):
+    def pivotIndex(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        total_sum = 0
+        left_sum = 0
+        
+        for num in nums:
+            total_sum += num
+            
+        for i in range(len(nums)):
+            right_sum = total_sum - nums[i] - left_sum
+            if left_sum == right_sum:
+                return i
+            left_sum += nums[i]
+            
+        return -1