SDUT 2139 图结构练习——BFS——从起始点到目标点的最短步数（BFS + vector）

#include<iostream>
#include<algorithm>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<queue>
#include<vector>

using namespace std;

const int maxn = 1001;

struct node
{
    int x;
    int ans;
};

int n,m;
vector<int>p[maxn];
int v[maxn];
int flag;

void BFS()
{
    memset(v,0,sizeof(v));
    queue<struct node>q;
    while(!q.empty())
    {
        q.pop();
    }
    struct node t,f;
    t.x = n;
    t.ans = 0;
    q.push(t);
    v[t.x] = 1;
    while(!q.empty())
    {
        t = q.front();
        q.pop();
        for(int i=0;i<p[t.x].size();i++)
        {
            if(v[p[t.x][i]] == 0)
            {
                f.x = p[t.x][i];
                f.ans = t.ans + 1;
                if(p[t.x][i] == 1)
                {
                    flag = f.ans;
                    return ;
                }
                q.push(f);
                v[p[t.x][i]] = 1;
            }
        }
    }
}

int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        flag = 0;
        for(int i=0;i<=n;i++)
        {
            p[i].clear();
        }
        int x,y;
        for(int i=0;i<m;i++)
        {
            scanf("%d%d",&x,&y);
            p[x].push_back(y);
        }
        BFS();
        if(flag)
        {
            printf("%d\n",flag);
        }
        else
        {
            printf("NO\n");
        }
    }
    return 0;
}