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("%dn", a)
#define plld(a) printf("%lldn", a)
#define pc(a) printf("%cn", a)
#define ps(a) printf("%sn", 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 = 2222222, 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] = 0;
vis[s] = 1;
while(!Q.empty())
{
int u = Q.front(); Q.pop_front();
vis[u] = 0;
for(int i = head[u]; i != -1; 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] = 1;
}
}
}
}
}
void init()
{
mem(head, -1);
g.clear();
cnt = 0;
}
void bfs()
{
queue<int> Q;
Q.push(1);
mem(vis, 0);
vis[1] = 1;
int cnt1 = 0;
while(!Q.empty())
{
int u = Q.front(); Q.pop();
for(int i = head[u]; i != -1; i = nex[i])
{
int v = Node[i].v;
if(d[v] == d[u] + Node[i].w)
{
if(!vis[v])
{
g.push_back((i + 2) / 2);
vis[v] = 1;
Q.push(v);
if(++cnt1 == k) return;
}
}
}
}
}
int main()
{
//
cout << 0x3f <<endl;

init();
int ans = 0;
int u, v, w;
cin >> n >> m >> k;
for(int i = 0; i < m; i++)
{
cin >> u >> v >> w;
add(u, v, w);
}
if(k == 0)
return puts("0");
s = 1;
spfa();
bfs();
cout << g.size() << endl;
for(int i = 0; i < g.size(); i++)
cout << g[i] << " ";
cout << endl;
return 0;
}