724_Find_Pivot_Index

qiyuangong · qiyuangong · commit b6ea0246b1f7 · 2018-12-05T18:26:40.000+08:00
diff --git a/README.md b/README.md
@@ -160,6 +160,7 @@ Also, there are open source implementations for basic data structs and algorithm
 | 709 | [To Lower Case](https://leetcode.com/problems/to-lower-case/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/709_To_Lower_Case.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/709_To_Lower_Case.java) | String processing:<br>1. str.lower() or str.toLowerCase()<br>2. ASCII processing. O(n) and O(1) |
 | 716 | [Max Stack](https://leetcode.com/problems/max-stack/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/716_Max_Stack.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/716_Max_Stack.java) | 1. Two stacks<br> 2. Double linked list and Hash |
 | 720 | [Longest Word in Dictionary](https://leetcode.com/problems/longest-word-in-dictionary/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/720_Longest_Word_in_Dictionary.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/720_Longest_Word_in_Dictionary.java) | 1. Brute Force, O(sum(w^2)) and O(w)<br>2. Tire Tree, O(sum(w) and O(w))<br>3. Sort and word without last char, O(nlogn + sum(w)) and O(w) |
+| 724 | [Find Pivot Index](https://leetcode.com/problems/find-pivot-index/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/724_Find_Pivot_Index.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/724_Find_Pivot_Index.java) | Seach the array to find a place where left sum is equal to right sum, O(n) and O(1) |
 | 743 | [Network Delay Time](https://leetcode.com/problems/network-delay-time/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/743_Network_Delay_Time.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/743_Network_Delay_Time.java) | Let V == N, then: 1. DFS, O(V^V+ElgE), O(V+E)<br>2. Dijkstra, O(V^2+E), O(V+E)|
 | 771 | [Jewels and Stones](https://leetcode.com/problems/jewels-and-stones/description/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/771_Jewels_and_Stones.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/771_Jewels_and_Stones.java) | Count given char in string. Hash or table. [Oneline](https://leetcode.com/problems/jewels-and-stones/discuss/113574/1-liners-PythonJavaRuby) |
 | 804 | [Unique Morse Code Words](https://leetcode.com/problems/unique-morse-code-words/description/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/804_Unique_Morse_Code_Words.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/804_Unique_Morse_Code_Words.java) | String, Hash and Set. Set is recommended. |
diff --git a/java/724_Find_Pivot_Index.java b/java/724_Find_Pivot_Index.java
@@ -0,0 +1,13 @@
+class Solution {
+    public int pivotIndex(int[] nums) {
+        int totalsum = 0, leftsum = 0;
+        // Compute total sum
+        for (int i = 0; i < nums.length; i++) totalsum += nums[i];
+        // Check leftsum == rightsum
+        for (int i = 0; i < nums.length; i++) {
+            if (leftsum == totalsum - leftsum - nums[i]) return i;
+            leftsum += nums[i];
+        }
+        return -1;
+    }
+}
diff --git a/python/724_Find_Pivot_Index.py b/python/724_Find_Pivot_Index.py
@@ -0,0 +1,14 @@
+class Solution(object):
+    def pivotIndex(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        totalsum = sum(nums)
+        leftsum = 0
+        for i, v in enumerate(nums):
+            # leftsum == rightsum
+            if leftsum == totalsum - leftsum - v:
+                return i
+            leftsum += v
+        return -1
