LeetCode-in-Java

498. Diagonal Traverse

Medium

Given an m x n matrix mat, return an array of all the elements of the array in a diagonal order.

Example 1:

Input: mat = [[1,2,3],[4,5,6],[7,8,9]]

Output: [1,2,4,7,5,3,6,8,9]

Example 2:

Input: mat = [[1,2],[3,4]]

Output: [1,2,3,4]

Constraints:

• m == mat.length
• n == mat[i].length
• 1 <= m, n <= 104
• 1 <= m * n <= 104
• -105 <= mat[i][j] <= 105

Solution

public class Solution {
    public int[] findDiagonalOrder(int[][] mat) {
        int m = mat.length;
        int n = mat[0].length;
        int[] output = new int[m * n];
        int idx = 0;
        for (int diag = 0; diag <= m + n - 2; ++diag) {
            if (diag % 2 == 0) {
                for (int k = Math.max(0, diag - m + 1); k <= Math.min(diag, n - 1); ++k) {
                    output[idx++] = mat[diag - k][k];
                }
            } else {
                for (int k = Math.max(0, diag - n + 1); k <= Math.min(diag, m - 1); ++k) {
                    output[idx++] = mat[k][diag - k];
                }
            }
        }
        return output;
    }
}

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