6.4.2 走迷宫

利用bfs寻找最短路。通过对u/m得到x，u%m得到y。u = x * m + y
将方向保存在dx[], dy[]中。

c
int q[maxn*maxn];
void bfs(int x, int y)
{int front = 0, rear = 0, d, u;u = x*m + y;vis[x][y] = 1; fa[x][y] = u; dist[x][y] = 0;q[rear++] = u;while(front < rear){u = q[front++];x = u/m; y = u %m;for(d = 0; d < 4; d++){int nx = x + dx[d], ny = y + dy[d];if (nx >= 0 && nx < n && ny >= 0 && ny <m && maze[nx][ny] && !vis[nx][ny]){int v= nx * m + ny;q[rear++] = v;vis[nx][ny] = 1;fa[nx][ny] = u;dist[nx][ny] = dist[x][y]+1;last_dir[nx][ny] = d;}}}
}

6.4.3 拓扑排序，DAG（Directed Acyclic Graph)有向无环图

c#include <stdio.h>
#include <string.h>const int maxn = 1000;
const int maxm = 1000;// 用于判断是否存在环
int c[maxn];
int topo[maxn], t;
int n, m;
int G[maxm][maxm];bool dfs(int u)
{c[u] = -1;for(int v= 0; v < n; v++) if(G[u][v]){if(c[v] < 0) return false;else if(!c[v] && !dfs(v)) return false;}c[u] = 1; topo[--t] = u;return true;
}bool toposort()
{t = n;memset(c, 0, sizeof(c));for(int u = 0; u < n; u++) if(!c[u])if(!dfs(u)) return false;return true;
}int main()
{int u, v;while(~scanf("%d %d", &n, &m)){memset(G, 0, sizeof(G));memset(topo, 0, sizeof(topo));for(int i = 0; i < m; i++){scanf("%d %d", &u, &v);G[u][v] = 1;}if(toposort()){for(int i = 0; i < n; i++)printf("%d ", topo[i]);printf("\n");} else {printf("sort error\n");}}return 0;
}