Code & Fun

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:

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

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

Example 2:

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

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

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:

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void rotate(vector<vector<int>>& matrix) {
int beg = 0, end = matrix.size() - 1;
int temp;
while(beg < end) {
int size = end - beg;
for(int i = 0;i < size;i++) {
temp = matrix[beg+i][beg];
matrix[beg+i][beg] = matrix[end][beg+i];
matrix[end][beg+i] = matrix[end-i][end];
matrix[end-i][end] = matrix[beg][end-i];
matrix[beg][end-i] = temp;
}
beg++; end--;
}
}

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