LeetCode in Kotlin

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

class Solution {
    fun findDiagonalOrder(mat: Array<IntArray>): IntArray {
        val m = mat.size
        val n = mat[0].size
        val output = IntArray(m * n)
        var idx = 0
        for (diag in 0..m + n - 2) {
            if (diag % 2 == 0) {
                for (k in Math.max(0, diag - m + 1)..Math.min(diag, n - 1)) {
                    output[idx++] = mat[diag - k][k]
                }
            } else {
                for (k in Math.max(0, diag - n + 1)..Math.min(diag, m - 1)) {
                    output[idx++] = mat[k][diag - k]
                }
            }
        }
        return output
    }
}

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