867. Transpose Matrix

867. Transpose Matrix (Easy)

Given a matrix A, return the transpose of A.

The transpose of a matrix is the matrix flipped over it's main diagonal, switching the row and column indices of the matrix.

Example 1:

Input: [[1,2,3],[4,5,6],[7,8,9]]
Output: [[1,4,7],[2,5,8],[3,6,9]]

Example 2:

Input: [[1,2,3],[4,5,6]]
Output: [[1,4],[2,5],[3,6]]

Note:

1. 1 <= A.length <= 1000
2. 1 <= A[0].length <= 1000

Solution 1.

// OJ: https://leetcode.com/problems/transpose-matrix/
// Author: github.com/lzl124631x
// Time: O(MN)
// Space: O(1)
class Solution {
public:
    vector<vector<int>> transpose(vector<vector<int>>& A) {
        if (A.empty() || A[0].empty()) return {};
        int M = A.size(), N = A[0].size();
        vector<vector<int>> v(N, vector<int>(M));
        for (int i = 0; i < M; ++i) {
            for (int j = 0; j < N; ++j) {
                v[j][i] = A[i][j];
            }
        }
        return v;
    }
};