867. Transpose Matrix

Posted 2020-12-27 gsz-

题目描述：

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

解题思路：

暴力遍历原来矩阵的每个元素，放到输出矩阵的对应位置。

由于veector的内存分配机制，由于已知输出矩阵的大小，所以在每个vector定义时指定空间大小会节省运行时间。

 

代码：

 1 class Solution {
 2 public:
 3     vector<vector<int>> transpose(vector<vector<int>>& A) {
 4         vector<vector<int> > res;
 5         res.reserve(A[0].size());
 6         for (int i = 0; i < A[0].size(); ++i) {
 7             vector<int> tmp;
 8             tmp.reserve(A.size());
 9             for (int j = 0; j < A.size(); ++j) {
10                 tmp.push_back(A[j][i]);
11             }
12             res.push_back(tmp);
13         }
14         return res;
15     }
16 };