Tyvj 1176 火焰巨魔的惆怅

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
#include<vector>
#include<queue>
using namespace std;
const int maxn = 100005;
const int maxint = ~0U>>1;
struct edge{
    int v;
    int w;
};
int n,m,vis[maxn],d[maxn];
vector<edge> g[maxn];
void input(){
    cin>>n>>m;
    int u,v,w;
    edge tmp;
    for(int i = 1;i <= m;i++){
        scanf("%d%d%d",&u,&v,&w);
        tmp.v = u;
        tmp.w = w;
        g[v].push_back(tmp);
    }
    for(int i = 1;i <= n;i++){
        vis[i] = 0;
        d[i] = maxint;
    }
}
void spfa(){
    queue<int> q;
    q.push(n);
    d[n] = 1;
    vis[n] = 1;
    int now,to,add;
    while(!q.empty()){
        now = q.front();
        q.pop();
        vis[now] = 0;
        for(int i = 0;i < g[now].size();i++){
            to = g[now][i].v;
            add = (d[now] - g[now][i].w) >> 1;
            if((d[now]-g[now][i].w) & 1) add++;
            if(add <= 0) add = 1;
            if(d[to] > add){
                d[to] = add;
                if(!vis[to]){
                    vis[to] = 1;
                    q.push(to);
                }
            }
        }
    }
}
 int main(){
    input();
    spfa();
    cout<<d[1];
    return 0;
}