1652. Defuse the Bomb

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Array

Time: O(n)

Space: O(n)

Intuition

Defuse bomb: each value is sum of k next (positive k) or k previous (negative k) elements. Circular array.

Algorithm

1If k==0: all zeros. If k>0: for each i, sum code[(i+1)...(i+k)] (circular). If k<0: sum code[(i-|k|)...(i-1)].
2Use prefix sums on doubled array for efficiency.

Common Pitfalls

•Handle circular indexing with modulo. k can be negative (look backward).

1652.cs

// Approach: Circular sliding window sum — use prefix sums on doubled array to handle wrap-around.
// Time: O(n) Space: O(n)

public class Solution
{
    public int[] Decrypt(int[] code, int k)
    {
        int n = code.Length;
        int[] ans = new int[n];
        if (k == 0)
            return ans;

        int sum = 0;
        int start = k > 0 ? 1 : n + k; // the start of the next k numbers
        int end = k > 0 ? k : n - 1;   // the end of the next k numbers

        for (int i = start; i <= end; ++i)
            sum += code[i];

        for (int i = 0; i < n; ++i)
        {
            ans[i] = sum;
            sum -= code[start++ % n];
            sum += code[++end % n];
        }

        return ans;
    }
}

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