Balance Point
Beginner
Return the leftmost index i where the sum of the values to its left equals the sum of the values to its right (the value at i itself is not counted). An empty side has sum 0. If no index works, return -1.
A simple solution adds up both sides for every index. It is correct but too slow for long lists. Make it fast.
Examples
Example 1
Input:
pivot_index([1, 7, 3, 6, 5, 6])
Output:
3
At index 3 the left sum is 1+7+3 = 11 and the right sum is 5+6 = 11.
Example 2
Input:
pivot_index([1, 2, 3])
Output:
-1
No index balances.
Constraints
0 <= len(nums) <= 2 * 10**5-10**4 <= nums[i] <= 10**4
Theory
Go to TheoryKeywords
dsa-sheetarraysarray-basics
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