Description#
Given a 0-indexed integer array nums, find the leftmost middleIndex (i.e., the smallest amongst all the possible ones).
A middleIndex is an index where nums[0] + nums[1] + ... + nums[middleIndex-1] == nums[middleIndex+1] + nums[middleIndex+2] + ... + nums[nums.length-1].
If middleIndex == 0, the left side sum is considered to be 0. Similarly, if middleIndex == nums.length - 1, the right side sum is considered to be 0.
Return the leftmost middleIndex that satisfies the condition, or -1 if there is no such index.
Example 1:
Input: nums = [2,3,-1,8,4]
Output: 3
Explanation: The sum of the numbers before index 3 is: 2 + 3 + -1 = 4
The sum of the numbers after index 3 is: 4 = 4
Example 2:
Input: nums = [1,-1,4]
Output: 2
Explanation: The sum of the numbers before index 2 is: 1 + -1 = 0
The sum of the numbers after index 2 is: 0
Example 3:
Input: nums = [2,5]
Output: -1
Explanation: There is no valid middleIndex.
Constraints:
1 <= nums.length <= 100-1000 <= nums[i] <= 1000
Note: This question is the same as 724: https://leetcode.com/problems/find-pivot-index/
Solutions#
Solution 1#
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| class Solution:
def findMiddleIndex(self, nums: List[int]) -> int:
left, right = 0, sum(nums)
for i, x in enumerate(nums):
right -= x
if left == right:
return i
left += x
return -1
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| class Solution {
public int findMiddleIndex(int[] nums) {
int left = 0, right = Arrays.stream(nums).sum();
for (int i = 0; i < nums.length; ++i) {
right -= nums[i];
if (left == right) {
return i;
}
left += nums[i];
}
return -1;
}
}
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| class Solution {
public:
int findMiddleIndex(vector<int>& nums) {
int left = 0, right = accumulate(nums.begin(), nums.end(), 0);
for (int i = 0; i < nums.size(); ++i) {
right -= nums[i];
if (left == right) {
return i;
}
left += nums[i];
}
return -1;
}
};
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| func findMiddleIndex(nums []int) int {
s := 0
for _, num := range nums {
s += num
}
total := 0
for i, num := range nums {
total += num
if total-num == s-total {
return i
}
}
return -1
}
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| function findMiddleIndex(nums: number[]): number {
let left = 0,
right = nums.reduce((a, b) => a + b);
for (let i = 0; i < nums.length; ++i) {
right -= nums[i];
if (left == right) {
return i;
}
left += nums[i];
}
return -1;
}
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| /**
* @param {number[]} nums
* @return {number}
*/
var findMiddleIndex = function (nums) {
let left = 0,
right = nums.reduce((a, b) => a + b);
for (let i = 0; i < nums.length; ++i) {
right -= nums[i];
if (left == right) {
return i;
}
left += nums[i];
}
return -1;
};
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