BFS与DFS机试模板

BFS的思想主要就是一层层扩散出去，使用一个辅助队列来实现，简单来讲就是每一步都要走可以走（判定边界，没走过等）的四个方向。

#include<bits/stdc++.h>
using namespace std;
const int maxn = 105;
char mpt[maxn][maxn];
int vis[maxn][maxn];
int dir[4][2] = {0,1,1,0,-1,0,0,-1};
struct node{
    int x,y;
    int step;
};
int bfs(int sx,int sy){
    memset(vis,0, sizeof(vis));
    queue<node> q;
    q.push(node{sx,sy,0});
    vis[sx][sy] = 1;
    int ans = 0;
    while (!q.empty()){
        node now = q.front();
        q.pop();
        if(mpt[now.x][now.y] == 'E'){
            ans = now.step;
            break;
        }
        for(int i = 0;i < 4;i++){
            int nx = now.x + dir[i][0];
            int ny = now.y + dir[i][1];
            if((mpt[nx][ny] == '*'||mpt[nx][ny] == 'E')&&vis[nx][ny] == 0){
                q.push(node{nx,ny,now.step+1});
                vis[nx][ny] = 1;
            }
        }
    }
    return ans;
}
int main(){
    int h,w;
    while (cin>>h>>w){
        int sx,sy;
        for(int i = 1;i <= h;i++){
            cin>>mpt[i]+1;
            for(int j = 1;j <= w;j++){
                if(mpt[i][j] == 'S')
                    sx = i, sy = j;
            }
        }
        int ans = bfs(sx,sy);
        cout<<ans<<endl;
    }
    return 0;
}

DFS，简单来说就是一条路走到底，走不通的时候回溯回来再走另一个方向，要注意回溯的时候要把走过的路标记为没走

#include<bits/stdc++.h>
using namespace std;
const int maxn = 105;
char mpt[maxn][maxn];
int vis[maxn][maxn];
int dir[4][2] = {1,0,0,1,-1,0,0,-1};
int ans;
void dfs(int x,int y,int step){
    if(step >= ans)return;//步数超过之前记录最短的就不用继续
    if(mpt[x][y] == 'E'){
        ans = min(ans,step);
        return;
    }
    for(int i = 0;i < 4;i++){
        int nx = x + dir[i][0];
        int ny = y + dir[i][1];
        if((mpt[nx][ny] == '*' || mpt[nx][ny] == 'E')&& vis[nx][ny] == 0){
            vis[nx][ny] = 1;
            dfs(nx,ny,step+1);
            vis[nx][ny] = 0;//回溯的时候标记为未走
        }
    }
}
int main(){
    int h,w;
    while (cin>>h>>w){
        if(h == 0 && w == 0)
            break;
        int sx = 0,sy = 0;
        memset(mpt,0, sizeof(mpt));
        memset(vis,0, sizeof(vis));
        for(int i = 1;i <= h;i++){
            cin>>mpt[i] + 1;
            for(int j = 1;j <= w;j++){
                if(mpt[i][j] == 'S')
                    sx = i, sy = j;
            }
        }
        ans = 999999;
        dfs(sx,sy,0);
        cout<<ans<<endl;
    }
    return 0;
}