1664. Ways to Make a Fair Array

 

Example 1:

Input: nums = [2,1,6,4]
Output: 1
Explanation:
Remove index 0: [1,6,4] -> Even sum: 1 + 4 = 5. Odd sum: 6. Not fair.
Remove index 1: [2,6,4] -> Even sum: 2 + 4 = 6. Odd sum: 6. Fair.
Remove index 2: [2,1,4] -> Even sum: 2 + 4 = 6. Odd sum: 1. Not fair.
Remove index 3: [2,1,6] -> Even sum: 2 + 6 = 8. Odd sum: 1. Not fair.
There is 1 index that you can remove to make nums fair.

Example 2:

Input: nums = [1,1,1]
Output: 3
Explanation: You can remove any index and the remaining array is fair.

Example 3:

Input: nums = [1,2,3]
Output: 0
Explanation: You cannot make a fair array after removing any index.

class Solution {

public int waysToMakeFair(int[] nums) {

int n = nums.length;

int rightOddSum = 0;

int rightEvenSum =0;

int res = 0;

for (int i = 0;i<n;i++){

if(i % 2 == 0){

rightEvenSum += nums[i];

}else{

rightOddSum += nums[i];

}

}

int leftEvenSum = 0;

int leftOddSum = 0;

for(int i = 0;i<n;i++){

if(i % 2 == 0){

rightEvenSum -= nums[i];

}else{

rightOddSum -= nums[i];

}

if(leftOddSum + rightEvenSum == leftEvenSum + rightOddSum){

res++;

}

if(i%2==0){

leftEvenSum += nums[i];

}else{

leftOddSum += nums[i];

}

}

return res;

}

}