LeetCode - Rotate Image
Problem description
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]
]
Analysis
The idea is simple, we do rotate from (i, i) to (i, n - 1 - i) each round for n/2 times.
Here’s the code:
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class Solution {
public void rotate(int[][] matrix) {
int n = matrix.length;
int round = n / 2;
for(int i = 0; i < round; i++){
for(int j = i; j < n - i - 1; j++){
int temp = matrix[i][j];
matrix[i][j] = matrix[n - 1 - j][i];
matrix[n - 1-j][i] = matrix[n - 1-i][n - 1-j];
matrix[n - 1-i][n - 1-j] = matrix[j][n - 1-i];
matrix[j][n - 1-i] = temp;
}
}
}
}
What to improve
- first think carefully then do the coding