2772. Apply Operations to Make All Array Elements Equal to Zero

You are given a 0-indexed integer array nums and a positive integer k.

You can apply the following operation on the array any number of times:

• Choose any subarray of size k from the array and decrease all its elements by 1.

Return true if you can make all the array elements equal to 0, or false otherwise.

A subarray is a contiguous non-empty part of an array.

class Solution {
public:
    bool checkArray(vector<int>& nums, int k) {
        vector<int> pre(nums.size() + 1);
        for(int i = 0; i < nums.size() - k + 1; i++) {
            if(i) pre[i] += pre[i-1];
            nums[i] -= pre[i];
            if(nums[i] < 0) return false;
            pre[i] += nums[i];
            pre[i+k] -= nums[i];
        }
        for(int i = nums.size() - k + 1; i < nums.size(); i++) {
            if(i) pre[i] += pre[i-1];
            nums[i] -= pre[i];
            if(nums[i] != 0) return false;
        }
        return true;
    }
};