LeetCode-in-Java

1329. Sort the Matrix Diagonally

Medium

A matrix diagonal is a diagonal line of cells starting from some cell in either the topmost row or leftmost column and going in the bottom-right direction until reaching the matrix’s end. For example, the matrix diagonal starting from mat[2][0], where mat is a 6 x 3 matrix, includes cells mat[2][0], mat[3][1], and mat[4][2].

Given an m x n matrix mat of integers, sort each matrix diagonal in ascending order and return the resulting matrix.

Example 1:

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

Output: [[1,1,1,1],[1,2,2,2],[1,2,3,3]]

Example 2:

Input: mat = [[11,25,66,1,69,7],[23,55,17,45,15,52],[75,31,36,44,58,8],[22,27,33,25,68,4],[84,28,14,11,5,50]]

Output: [[5,17,4,1,52,7],[11,11,25,45,8,69],[14,23,25,44,58,15],[22,27,31,36,50,66],[84,28,75,33,55,68]]

Constraints:

• m == mat.length
• n == mat[i].length
• 1 <= m, n <= 100
• 1 <= mat[i][j] <= 100

Solution

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Solution {
    public int[][] diagonalSort(int[][] mat) {
        int m = mat.length;
        int n = mat[0].length;
        int[][] sorted = new int[m][n];
        for (int i = m - 1; i >= 0; i--) {
            int iCopy = i;
            List<Integer> list = new ArrayList<>();
            for (int j = 0; j < n && iCopy < m; j++, iCopy++) {
                list.add(mat[iCopy][j]);
            }
            Collections.sort(list);
            iCopy = i;
            for (int j = 0; j < n && iCopy < m; j++, iCopy++) {
                sorted[iCopy][j] = list.get(j);
            }
        }

        for (int j = n - 1; j > 0; j--) {
            int jCopy = j;
            List<Integer> list = new ArrayList<>();
            for (int i = 0; i < m && jCopy < n; i++, jCopy++) {
                list.add(mat[i][jCopy]);
            }
            Collections.sort(list);
            jCopy = j;
            for (int i = 0; i < m && jCopy < n; i++, jCopy++) {
                sorted[i][jCopy] = list.get(i);
            }
        }
        return sorted;
    }
}

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