hdu 1839 Delay Constrained Maximum Capacity Path

最短路+二分。

对容量进行二分，因为容量和时间是单调关系的，容量越多，能用的边越少，时间会不变或者增加。

因为直接暴力一个一个容量去算会TLE，所以采用二分。

#include<cstdio>
#include<vector>
#include<cstring>
#include<queue>
#include<map>
#include<algorithm>
using namespace std;

const int maxn = 10001;
const int INF = 0x7FFFFFFF;
struct aaa { int u, v, cc, tt; }node[500005];
vector<aaa>ljb[maxn];
int c[500005], dist[maxn], flag[maxn];
int n, m, t;

void spfa(int xianzhi)
{
    int iii;
    queue<int>Q;
    memset(flag, 0, sizeof(flag));
    for (iii = 0; iii<=n; iii++) dist[iii] = INF;
    dist[1] = 0; Q.push(1); flag[1] = 1;
    while (!Q.empty())
    {
        int h = Q.front(); Q.pop(); flag[h] = 0;
        for (iii = 0; iii<ljb[h].size(); iii++)
        {
            aaa u = ljb[h][iii];
            if (u.cc >= xianzhi)
            {
                if (u.u == h)
                {
                    if (dist[u.u] + u.tt <= dist[u.v])
                    {
                        dist[u.v] = dist[u.u] + u.tt;
                        if (flag[u.v] == 0)
                        {
                            Q.push(u.v);
                            flag[u.v] = 1;
                        }
                    }
                }
                else if (u.v == h)
                {
                    if (dist[u.v] + u.tt <= dist[u.u])
                    {
                        dist[u.u] = dist[u.v] + u.tt;
                        if (flag[u.u] == 0)
                        {
                            Q.push(u.u);
                            flag[u.u] = 1;
                        }
                    }
                }
            }
        }
    }
}

int main()
{
    int X;
    scanf("%d", &X);
    while (X--)
    {
        int i, j, u, v, tt;
        scanf("%d%d%d", &n, &m, &t);
        for (i = 0; i <= n; i++) ljb[i].clear();
        for (i = 0; i <= m; i++) node[i].tt = INF;
        for (i = 0; i < m; i++)
        {
            scanf("%d%d%d%d", &u, &v, &c[i], &tt);
            node[i].u = u; node[i].v = v;
            node[i].cc = c[i]; node[i].tt = tt;
            ljb[v].push_back(node[i]); ljb[u].push_back(node[i]);
        }
        sort(c, c + m);
        int anss = -1, xx, dd, zz;
        xx = 0; dd = m - 1; zz = (xx + dd) / 2;
        while (1)
        {            
            spfa(c[zz]);
            if (dist[n] <= t) { anss = zz; xx = zz + 1; zz = (xx + dd) / 2; }
            else { dd = zz; zz = (xx + dd) / 2; }
            if (xx >= dd) break; 
        }
        printf("%d
", c[anss]);
    }
    return 0;
}