1329. Sort the Matrix Diagonally

# 1329. Sort the Matrix Diagonally#

## 题目 #

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]]
``````

Constraints:

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

## 解题思路 #

• 这道题思路很简单。按照对角线，把每条对角线的元素读取出来放在数组中。这里可以利用 map 保存这些数组。再将这些数组排序。最后按照对角线还原矩阵即可。

## 代码 #

``````package leetcode

func diagonalSort(mat [][]int) [][]int {
m, n, diagonalsMap := len(mat), len(mat[0]), make(map[int][]int)
for i := 0; i < m; i++ {
for j := 0; j < n; j++ {
diagonalsMap[i-j] = append(diagonalsMap[i-j], mat[i][j])
}
}
for _, v := range diagonalsMap {
sort.Ints(v)
}
for i := 0; i < m; i++ {
for j := 0; j < n; j++ {
mat[i][j] = diagonalsMap[i-j][0]
diagonalsMap[i-j] = diagonalsMap[i-j][1:]
}
}
return mat
}
``````

Apr 8, 2023