# 1329. Sort the Matrix Diagonally

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

class Solution {
public:
vector<vector<int>> diagonalSort(vector<vector<int>>& mat) {
int m = mat.size(), n = mat[0].size();
unordered_map<int, vector<int>> diagMap;
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
diagMap[i - j].push_back(mat[i][j]);
}
}
for (auto &a : diagMap) {
sort(a.second.rbegin(), a.second.rend());
}
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
mat[i][j] = diagMap[i - j].back();
diagMap[i - j].pop_back();
}
}
return mat;
}
};

Github 同步地址:

https://github.com/grandyang/leetcode/issues/1329

https://leetcode.com/problems/sort-the-matrix-diagonally/

https://leetcode.com/problems/sort-the-matrix-diagonally/solutions/489749/java-python-straight-forward/

https://leetcode.com/problems/sort-the-matrix-diagonally/solutions/489775/c-elegant-map-solution-easy-to-understand/

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