关于矩阵旋转，在不修改main()里面的代码的情况下，如何优化，可不可以再减少一些循环次数？

Question

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>

int a[4][4];
void RotateLeft(int(&inout)[4][4])
{
	for (int y = 0; y <4; y++){
		for (int x = 0; x < 4; x++){
			a[y][x] = inout[x][4-1-y];
		}
	}
	for (int y = 0; y < 4; y++) {
		for (int x = 0; x < 4; x++) {
			inout[y][x] =a[y][x];
		}
	}
}

void Output(int(&a)[4][4])
{	
	for (int y = 0; y < 4; ++y){
		for (int x = 0; x < 4; ++x){	
			printf("%3d", a[y][x]);
		}
		puts("");
	}
}

int main()
{
	int a[4][4] =
	{
		{  0,  1,  2,  3},
		{  4,  5,  6,  7},
		{  8,  9, 10, 11},
		{ 12, 13, 14, 15},
	};
	Output(a);
	for (int i = 0; i < 4; i++){
		puts("== Rotate left ==");
		RotateLeft(a);
		Output(a);
	}
}

Answer 1

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>

void RotateLeft(int(&inout)[4][4])
{
    int temp;
	for (int y = 0; y < 4/2; y++){ //减少循环次数，一次循环里面同时处理多个坐标的变换
		for (int x = y; x <4-1-y; x++){
		    temp = inout[y][x];
		    inout[y][x] = inout[x][4-1-y];
		    inout[x][4-1-y] = inout[4-1-y][4-1-x];
		    inout[4-1-y][4-1-x] = inout[4-1-x][y];
		    inout[4-1-x][y] = temp;
		}
	}
}

void Output(int(&inout)[4][4])
{	
	for (int y = 0; y < 4; ++y){
		for (int x = 0; x < 4; ++x){	
			printf("%3d", inout[y][x]);
		}
		puts("");
	}
}

int main()
{
	int a[4][4] =
	{
		{  0,  1,  2,  3},
		{  4,  5,  6,  7},
		{  8,  9, 10, 11},
		{ 12, 13, 14, 15},
	};
	Output(a);
	for (int i = 0; i < 4; i++){
		puts("== Rotate left ==");
		RotateLeft(a);
		Output(a);
	}
}