Code & Func

第92天。

今天的题目是Rotate Image:

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Note: You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

1
Given input matrix =
2
[
3
  [1,2,3],
4
  [4,5,6],
5
  [7,8,9]
6
],
7

8
rotate the input matrix in-place such that it becomes:
9
[
10
  [7,4,1],
11
  [8,5,2],
12
  [9,6,3]
13
]

Example 2:

1
Given input matrix =
2
[
3
  [ 5, 1, 9,11],
4
  [ 2, 4, 8,10],
5
  [13, 3, 6, 7],
6
  [15,14,12,16]
7
],
8

9
rotate the input matrix in-place such that it becomes:
10
[
11
  [15,13, 2, 5],
12
  [14, 3, 4, 1],
13
  [12, 6, 8, 9],
14
  [16, 7,10,11]
15
]

虽然是一道Medium的题目，但是还是比较简单的。

主要的思路是一圈一圈的进行旋转，不断缩减，直到不需要旋转的时候：

1
void rotate(vector<vector<int>>& matrix) {
2
    int beg = 0, end = matrix.size() - 1;
3
    int temp;
4
    while(beg < end) {
5
        int size = end - beg;
6
        for(int i = 0;i < size;i++) {
7
            temp = matrix[beg+i][beg];
8
            matrix[beg+i][beg] = matrix[end][beg+i];
9
            matrix[end][beg+i] = matrix[end-i][end];
10
            matrix[end-i][end] = matrix[beg][end-i];
11
            matrix[beg][end-i] = temp;
12
        }
13
        beg++; end--;
14
    }
15
}