HackerRank Java7求解对角线差遇运行时错误，请求代码排查

数据老陈

2026-5-25

Fixing the Runtime Error in Your Diagonal Difference Code

Hey there! I see you're just starting out on HackerRank and ran into a runtime error with your Diagonal Difference solution—let's get this sorted out quickly.

The Root Cause of the Runtime Error

Your code's issue comes down to an array index out of bounds in this line:

sum2 += a[n-i][i];

When i = 0, n - i equals n, but array indices start at 0. Since your matrix is n x n, the largest valid row index is n-1. Accessing a[n][0] tries to reach a row that doesn't exist, which triggers the runtime error.

The Correct Approach for the Reverse Diagonal

The reverse diagonal (from top-right to bottom-left) uses indices where the row index decreases as the column index increases. For each i (starting at 0), the correct row index is n-1 - i.

Fixed Code

Here's the corrected version of your function:

static int diagonalDifference(int[][] a) {
    int sum1 = 0;
    int sum2 = 0;
    int n = a[0].length;
    for(int i = 0; i < n; i++){
        sum1 += a[i][i];
        // Fixed the row index for the reverse diagonal
        sum2 += a[n-1 - i][i];
    }
    return Math.abs(sum1 - sum2);
}