1652. Defuse the Bomb

/* SLIDING WINDOW O(n) */
class Solution {
    public int[] decrypt(int[] code, int k) {
        int n = code.length;
        int ans[] = new int[n];
        if(k==0) return ans;
        int l = 1, r= k, sum = 0;
        if(k<0){    //If k<0, the starting point will be end of the array
            l =  n - Math.abs(k);
            r= n - 1;
        }
        for (int i=l; i<=r; i++) sum+=code[i];  //sum for the first window
        for (int i=0; i<n; i++){
            ans[i] = sum;
            sum -= code[(l) % n];   //removing the first elementto shorten the window
            sum += code[(r+ 1) % n];    //adding the next element to extend the widnow
            l++;
            r++;
        }
        return ans;
    }
}

/*
LOGIC---
For positive k, we start by calculating the sum of the first k elements and store it in result[0]. Let’s call this initial sum sum. 
As we shift the window to each new index, we update sum by subtracting the element that's leaving the window and adding the new element entering it. 
We repeat this process until we cover all indices and store each updated sum in result.

Similarly, when k is negative, we calculate the sum of the |k| elements preceding each index, beginning with the last |k| elements for the first index. 
Then, for each subsequent index, we update the sum by adjusting for the outgoing and incoming elements as before. 

After visiting all indices, we return the result array.

*/


/*  BRUTE FROCE O(n^2) */
class Solution {
    public int[] decrypt(int[] code, int k) {
        int n = code.length;
        int ans[] = new int[n];
        if(k==0) return ans;
        else if(k>0){
            for(int i=0;i<n;i++){
                int sum=0;
                int start=i+1;
                for(int j=0;j<k;j++){
                    if(start==n) start=0;
                    sum+=code[start];
                    start++;
                }
                ans[i]=sum;
            }
        }
        else if(k<0){
            for(int i=0;i<n;i++){
                int sum=0;
                int start=i-1;
                for(int j=0;j<Math.abs(k);j++){
                    if(start==-1) start=n-1;
                    sum+=code[start];
                    start--;
                }
                ans[i]=sum;
            }
        }
        return ans;
    }
}