题目

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:

image.png

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

Constraints:

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

题意

将一个矩阵的元素按照对角线进行排序。

思路

直接将每个对角线拉出来放入一个数组，排序后再放回即可。

代码实现

Java

  1. class Solution {
  2.     public int[][] diagonalSort(int[][] mat) {
  3.         int m = mat.length, n = mat[0].length;
  4.         for (int i = 0; i < m; i++) {
  5.             sort(mat, i, 0);
  6.         }
  7.         for (int i = 1; i < n; i++) {
  8.             sort(mat, 0, i);
  9.         }
  10.         return mat;
  11.     }
  13.     private void sort(int[][] mat, int i, int j) {
  14.         int m = mat.length, n = mat[0].length;
  15.         int size = Math.min(m - i, n - j);
  16.         int[] tmp = new int[size];
  17.         for (int k = 0; k < size; k++) {
  18.             tmp[k] = mat[i + k][j + k];
  19.         }
  20.         Arrays.sort(tmp);
  21.         for (int k = 0; k < size; k++) {
  22.             mat[i + k][j + k] = tmp[k];
  23.         }
  24.     }
  25. }