題目鏈接：http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=4020

很簡單的一個bfs題，是我想多了。

順便學習一下C++的STL中的vector的用法：https://www.cnblogs.com/youpeng/p/10779019.html

#include <cstdio>
#include <vector>
#include <queue>

using namespace std;

const int maxn = 300005;

vector<int> vec[maxn];
vector<bool> vis[maxn];

//前兩個是橫著走，後兩個是豎著走
int gox[4] = {0, 0, -1, 1};
int goy[4] = {-1, 1, 0, 0};

int test;
int n, m;
int sx, sy, ex, ey;

struct node {
    int x, y;
    int dis;
};

bool judge(node nex) {
    if (nex.x < 1 || nex.x > n || nex.y < 1 || nex.y > m || vis[nex.x][nex.y])
        return false;
    else
        return true;
}

int bfs() {
    node cu, ne;
    cu.x = sx, cu.y = sy;
    cu.dis = 0;
    vis[cu.x][cu.y] = true;
    queue<node> q;
    q.push(cu);
    while (!q.empty()) {
        cu = q.front();
        q.pop();

        //判斷是否滿足條件
        if (cu.x == ex && cu.y == ey) {
            return cu.dis;
        }

        int status = vec[cu.x][cu.y];
        if (cu.dis % 2) {
            if (status)
                status = 0;
            else
                status = 1;
        }

        if (status) { //橫著走
            for (int i = 0; i < 2; i++) {
                ne.x = cu.x + gox[i];
                ne.y = cu.y + goy[i];
                if (judge(ne)) {
                    vis[ne.x][ne.y] = true;
                    ne.dis = cu.dis + 1;
                    q.push(ne);
                }
            }
        } else { //豎著走
            for (int i = 2; i < 4; i++) {
                ne.x = cu.x + gox[i];
                ne.y = cu.y + goy[i];
                if (judge(ne)) {
                    vis[ne.x][ne.y] = true;
                    ne.dis = cu.dis + 1;
                    q.push(ne);
                }
            }
        }
    }
    return -1;
}

int main() {
    scanf("%d", &test);
    while (test--) {
        scanf("%d%d", &n, &m);
        for (int i = 0; i <= n; i++) {
            vec[i].clear();
            vis[i].clear();
        }

        int x;
        for (int i = 1; i <= n; i++) {
            vec[i].push_back(0);
            vis[i].push_back(false);
            for (int j = 1; j <= m; j++) {
                scanf("%d", &x);
                vec[i].push_back(x);
                vis[i].push_back(false);
            }
        }
        scanf("%d%d%d%d", &sx, &sy, &ex, &ey);
        int ans = bfs();
        if (ans >= 0) {
            printf("%d\n", ans);
        } else {
            printf("-1\n");
        }
    }
    return 0;
}
 

[ZOJ 4020] Traffic Light