Edge Deletion CodeForces - 1076D（水最短路）

题意：

　　设从1到每个点的最短距离为d，求删除几条边后仍然使1到每个点的距离为d，使得剩下的边最多为k

解析：

　　先求来一遍spfa，然后bfs遍历每条路，如果d[v] == d[u] + Node[i].w 则说明这条路要保留

　　注意是按着走的路的顺序输出的 wa1

　　注意最大值设为0x3f  wa3  学到了。。。emm 用memset设置数组为0x3f是无穷大

#include <iostream>
#include <cstdio>
#include <sstream>
#include <cstring>
#include <map>
#include <cctype>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#include <bitset>
#include <limits.h>
#define rap(i, a, n) for(int i=a; i<=n; i++)
#define rep(i, a, n) for(int i=a; i<n; i++)
#define lap(i, a, n) for(int i=n; i>=a; i--)
#define lep(i, a, n) for(int i=n; i>a; i--)
#define rd(a) scanf("%d", &a)
#define rlld(a) scanf("%lld", &a)
#define rc(a) scanf("%c", &a)
#define rs(a) scanf("%s", a)
#define rb(a) scanf("%lf", &a)
#define rf(a) scanf("%f", &a)
#define pd(a) printf("%d\n", a)
#define plld(a) printf("%lld\n", a)
#define pc(a) printf("%c\n", a)
#define ps(a) printf("%s\n", a)
#define MOD 2018
#define LL long long
#define ULL unsigned long long
#define Pair pair<int, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define _  ios_base::sync_with_stdio(0),cin.tie(0)
//freopen("1.txt", "r", stdin);
using namespace std;
const int maxn = , INF = 0x7fffffff;

int head[maxn], vis[maxn], nex[maxn];
LL d[maxn];
int cnt, n, m, s, t, k;
vector<int> g;

struct node
{
    int u, v;
    LL w;
}Node[maxn];

void add_(int u, int v, int w)
{
    Node[cnt].u = u;
    Node[cnt].v = v;
    Node[cnt].w = w;
    nex[cnt] = head[u];
    head[u] = cnt++;
}

void add(int u, int v, int w)
{
    add_(u, v, w);
    add_(v, u, w);
}

int spfa()
{
    mem(d, 0x3f);
    deque<int> Q;
    Q.push_front(s);
    d[s] = ;
    vis[s] = ;
    while(!Q.empty())
    {
        int u = Q.front(); Q.pop_front();
        vis[u] = ;
        for(int i = head[u]; i != -; i = nex[i])
        {
            int v = Node[i].v;
            if(d[v] > d[u] + Node[i].w)
            {
                d[v] = d[u] + Node[i].w;
                if(!vis[v])
                {
                    if(Q.empty()) Q.push_front(v);
                    else
                    {
                        if(d[v] < d[Q.front()]) Q.push_front(v);
                        else Q.push_back(v);
                    }
                    vis[v] = ;
                }
            }
        }
    }
}

void init()
{
    mem(head, -);
    g.clear();
    cnt = ;
}

void bfs()
{
    queue<int> Q;
    Q.push();
    mem(vis, );
    vis[] = ;
    int cnt1 = ;
    while(!Q.empty())
    {
        int u = Q.front(); Q.pop();
        for(int i = head[u]; i != -; i = nex[i])
        {
            int v = Node[i].v;
            if(d[v] == d[u] + Node[i].w)
            {
                if(!vis[v])
                {
                    g.push_back((i + ) / );
                    vis[v] = ;
                    Q.push(v);
                    if(++cnt1 == k) return;
                }
            }
        }
    }
}

int main()
{
     //   cout << 0x3f <<endl;
    init();
    int ans = ;
    int u, v, w;
    cin >> n >> m >> k;
    for(int i = ; i < m; i++)
    {
        cin >> u >> v >> w;
        add(u, v, w);
    }
    if(k == )
        return puts("");
    s = ;
    spfa();
    bfs();

    cout << g.size() << endl;
    for(int i = ; i < g.size(); i++)
        cout << g[i] << " ";
    cout << endl;

    return ;
}