3. 深度优先搜索

现在我们用堆栈解决一个有意思的问题，定义一个二维数组：

int maze[5][5] = {
    0, 1, 0, 0, 0,
    0, 1, 0, 1, 0,
    0, 0, 0, 0, 0,
    0, 1, 1, 1, 0,
    0, 0, 0, 1, 0,
};

它表示一个迷宫，其中的1表示墙壁，0表示可以走的路，只能横着走或竖着走，不能斜着走，要求编程序找出从左上角到右下角的路线。程序如下：

#include <stdio.h>

#define MAX_ROW 5
#define MAX_COL 5

struct point { int row, col; } stack[512];
int top = 0;

void push(struct point p)
{
    stack[top++] = p;
}

struct point pop(void)
{
    return stack[--top];
}

int is_empty(void)
{
    return top == 0;
}

int maze[MAX_ROW][MAX_COL] = {
    0, 1, 0, 0, 0,
    0, 1, 0, 1, 0,
    0, 0, 0, 0, 0,
    0, 1, 1, 1, 0,
    0, 0, 0, 1, 0,
};

void print_maze(void)
{
    int i, j;
    for (i = 0; i < MAX_ROW; i++) {
        for (j = 0; j < MAX_COL; j++)
            printf("%d ", maze[i][j]);
        putchar('\n');
    }
    printf("*********\n");
}

struct point predecessor[MAX_ROW][MAX_COL] = {
    {{-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}},
    {{-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}},
    {{-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}},
    {{-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}},
    {{-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}, {-1,-1}},
};

void visit(int row, int col, struct point pre)
{
    struct point visit_point = { row, col };
    maze[row][col] = 2;
    predecessor[row][col] = pre;
    push(visit_point);
}

int main(void)
{
    struct point p = { 0, 0 };

    maze[p.row][p.col] = 2;
    push(p);    
    
    while (!is_empty()) {
        p = pop();
        if (p.row == MAX_ROW - 1  /* goal */
            && p.col == MAX_COL - 1)
            break;
        if (p.col+1 < MAX_COL     /* right */
            && maze[p.row][p.col+1] == 0)
            visit(p.row, p.col+1, p);
        if (p.row+1 < MAX_ROW     /* down */
            && maze[p.row+1][p.col] == 0)
            visit(p.row+1, p.col, p);
        if (p.col-1 >= 0          /* left */
            && maze[p.row][p.col-1] == 0)
            visit(p.row, p.col-1, p);
        if (p.row-1 >= 0          /* up */
            && maze[p.row-1][p.col] == 0)
            visit(p.row-1, p.col, p);
        print_maze();
    }
    if (p.row == MAX_ROW - 1 && p.col == MAX_COL - 1) {
        printf("(%d, %d)\n", p.row, p.col);
        while (predecessor[p.row][p.col].row != -1) {
            p = predecessor[p.row][p.col];
            printf("(%d, %d)\n", p.row, p.col);
        }
    } else
        printf("No path!\n");

    return 0;
}

运行结果如下：

3. 深度优先搜索 ​

3. 深度优先搜索