（一）深搜法：

1.遞迴的邊界：

走到終點座標， 即(x == x2 && y == y2)；

2.遞迴進行的條件：

for迴圈的 4個方向（定義了一個方向陣列move）進行遞迴：

判斷條件：若為路 && 未標記 && 不越界, 則繼續遞迴;即(A[x][y] == 0 && flag[x][y] == 0 && x >= 0 && x <= 8 && y >= 0 && y <= 8)

在走的過程中，要注意標記和清除走過的點，還原走過的位置。

程式碼1：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int A[9][9] = {
	 1,1,1,1,1,1,1,1,1,
	 1,0,0,1,0,0,1,0,1,
	 1,0,0,1,1,0,0,0,1,
	 1,0,1,0,1,1,0,1,1,
	 1,0,0,0,0,1,0,0,1,
	 1,1,0,1,0,1,0,0,1,
	 1,1,0,1,0,1,0,0,1,
	 1,1,0,1,0,0,0,0,1,
	 1,1,1,1,1,1,1,1,1};
int flag[9][9];//flag標記陣列;
int min = 0x7FFFFFFF, sum1 = 0;
typedef struct item
{
	int x;
	int y;
}dir;
dir move[4] = {1, 0, 0, -1, -1, 0, 0, 1};//方向陣列;
void walking(int x, int y, int x2, int y2,int sum);

int main(void)
{
	int N;
	scanf("%d", &N);
	while(N--)
	{
		int x1, y1, x2, y2;
		scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
		walking(x1, y1, x2, y2,0);
		printf("min = %d\n", min);
		//sum = 0;
		min = 0x7FFFFFFF;
		memset(flag, 0, sizeof(flag));
	}
	return 0;
}
void walking(int x, int y, int x2, int y2,int sum)//(x,y)當前座標,(x2, y2)終點座標
{
	int i;
	if(x == x2 && y == y2)//遞迴結束;
	{
		if(sum < min)
			min = sum;
		return ;
	}
//	if(0 <= x || x >= 8 || 0 <= y || y >= 8)//已經走過 or 越界;
//		return ;
	for(i = 0; i < 4; i++)
	{
		x = x + move[i].x;
		y = y + move[i].y;
		if(x >= 0 && x <= 8 && y >= 0 && y <= 8 && A[x][y] == 0 && flag[x][y] == 0)//若為路，繼續遞迴;
		{
			flag[x][y] = 1;
			//sum++;
			walking(x, y, x2, y2,sum + 1);
			flag[x][y] = 0;
			x = x - move[i].x;
			y = y - move[i].y;
		//	sum--;
		}
	}//for
}
 

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int A[9][9]  = {//0路1牆;
	 1,1,1,1,1,1,1,1,1,
	 1,0,0,1,0,0,1,0,1,
	 1,0,0,1,1,0,0,0,1,
	 1,0,1,0,1,1,0,1,1,
	 1,0,0,0,0,1,0,0,1,
	 1,1,0,1,0,1,0,0,1,
	 1,1,0,1,0,1,0,0,1,
	 1,1,0,1,0,0,0,0,1,
	 1,1,1,1,1,1,1,1,1};
int flag[9][9];//flag標記陣列;
int min,x2, y2;//將終點定義為全域性變數;
typedef struct item
{
	int x;
	int y;
}dir;
dir move[4] = {1, 0, 0, -1, -1, 0, 0, 1};//方向陣列;
void walking(int x, int y, int sum);//精簡遞迴函式,引數中和只有變化的量;sum代表當前走了多少步;
int main(void)
{
	int N;
	scanf("%d", &N);
	while(N--)
	{
		int x1, y1;//每次迴圈開始前進行初始化;
		min = 0x7FFFFFFF;
		memset(flag, 0, sizeof(flag));
		scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
		walking(x1, y1, 0);
		printf("%d\n", min);
	}
	return 0;
}
void walking(int x, int y, int sum)
{
	int i;
	if(x == x2 && y == y2)//遞迴結束;
	{
		if(sum < min)
			min = sum;
		return ;
	}
	for(i = 0; i < 4; i++)
	{
		x = x + move[i].x;
		y = y + move[i].y;
		if(A[x][y] == 0 && flag[x][y] == 0 && x >= 0 && x <= 8 && y >= 0 && y <= 8)//若為路 && 未標記 && 不越界, 則繼續遞迴;
		{
			flag[x][y] = 1;
			walking(x, y, sum + 1);
			flag[x][y] = 0;
		}
		x = x - move[i].x;//***
		y = y - move[i].y;//***
	}//for
}
 

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int A[9][9] = {
	 1,1,1,1,1,1,1,1,1,
	 1,0,0,1,0,0,1,0,1,
	 1,0,0,1,1,0,0,0,1,
	 1,0,1,0,1,1,0,1,1,
	 1,0,0,0,0,1,0,0,1,
	 1,1,0,1,0,1,0,0,1,
	 1,1,0,1,0,1,0,0,1,
	 1,1,0,1,0,0,0,0,1,
	 1,1,1,1,1,1,1,1,1};
int flag[9][9];//flag標記陣列;
int min;
typedef struct item
{
	int x;
	int y;
}dir;
int move[8] = {1, 0, 0, -1, -1, 0, 0, 1};//方向陣列;
void walking(int x, int y, int x2, int y2,int sum);

int main(void)
{
	int N;
	scanf("%d", &N);
	while(N--)
	{
		int x1, y1, x2, y2;

		min = 0x7FFFFFFF;
		memset(flag, 0, sizeof(flag));
scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
		walking(x1, y1, x2, y2,0);
		printf("min = %d\n", min);
	}
	return 0;
}
void walking(int x, int y, int x2, int y2,int sum)//(x,y)當前座標,(x2, y2)終點座標
{
	int i;
	if(x == x2 && y == y2)//遞迴結束;
	{
		if(sum < min)
			min = sum;
		return ;
	}

	for(i = 0; i < 8; i+= 2)
	{
		x += move[i];
		y += move[i + 1];
		if(x >= 0 && x <= 8 && y >= 0 && y <= 8 && A[x][y] == 0 && flag[x][y] == 0)//若為路，繼續遞迴;
		{
			flag[x][y] = 1;		
			walking(x, y, x2, y2,sum + 1);
			flag[x][y] = 0;
			
		}
		x -= move[i];
		y -= move[i + 1];
	}//for
}