Array elements rotate clockwise
leetcode: 48. Rotate image
Medium difficulty
Given an n × n two-dimensional matrix represents an image.
Rotate the image 90 degrees clockwise.
Description:
You have to rotate the image **in place **, which means you need to modify the input 2D matrix directly. Please do not use another matrix to rotate the image.
Example 1:
给定 matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],
原地旋转输入矩阵，使其变为:
[
[7,4,1],
[8,5,2],
[9,6,3]
]
Example 2:
给定 matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],
原地旋转输入矩阵，使其变为:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]
Problem-solving ideas:
Understand the essence of the problem—>Abstract the big problem, summarize the law of change—>Realize—>Optimize operation speed
Array is divided into units by circle
Determine the coordinates of the upper left and lower right corners, and then "shrink the circle"
Rotate the elements of each layer at right angles
The inner elements are operated with the outer elements. Until startX>endX
Test code:
package main
import "fmt"
func main() {
print := func(nums [][]int) {
for _, v := range nums {
for _, n := range v {
fmt.Print("\t", n)
}
fmt.Println()
}
fmt.Println("---------------")
}
nums := [][]int{
{
1, 2, 3, 4}, {
5, 6, 7, 8}, {
9, 10, 11, 12}, {
13, 14, 15, 16}}
print(nums)
startX ,startY, endX ,endY := 0,0,len(nums[0]) - 1, len(nums[0]) - 1
for startX < endX {
for i := 0; i < endX-startX; i++ {
nums[startX][startY+i], nums[endX-i][startY], nums[endX][endY-i], nums[startX+i][endY] =
nums[endX-i][startY], nums[endX][endY-i], nums[startX+i][endY], nums[startX][startY+i]
}
startX,startY,endX,endY = startX+1,startY+1,endX-1,endY-1
}
print(nums)
}
/*
00 01 02 03
10 11 12 13
20 21 22 23
30 31 32 33
tmp=00
00=30
30=33
33=03
03=tmp
*/
The function entry provided by leetcode, I replaced the parameter variable
func rotate(nums [][]int) {
startX ,startY, endX ,endY := 0,0,len(nums[0]) - 1, len(nums[0]) - 1
for startX < endX {
for i := 0; i < endX-startX; i++ {
nums[startX][startY+i], nums[endX-i][startY], nums[endX][endY-i], nums[startX+i] [endY] =
nums[endX-i][startY], nums[endX][endY-i], nums[startX+i][endY], nums[startX][startY+i]
}
startX,startY,endX,endY = startX+1,startY+1,endX-1,endY-1
}
}
Full change map
Shuichi Shita
