luogu P1396营救

Posted 2020-10-07 ssttkkl

https://www.luogu.org/problem/show?pid=1396

弱化版的货车运输，用并查集维护连通块，将边按权值升序排序后依次插入直到两点连通，最后插入的边的权值就是最小的拥挤度最大值。

#include <iostream>
#include <vector>
#include <algorithm>
#define maxn 100005
using namespace std;
int n, m, s, t;
struct edge
{
    int from, to, weight;
};
bool operator<(const edge &x, const edge &y)
{
    return x.weight < y.weight;
}
vector<edge> e;
namespace djs
{
int parent[maxn];
void init()
{
    for (int i = 1; i <= n; i++)
        parent[i] = -1;
}
int find(int x)
{
    if (parent[x] < 0)
        return x;
    else
        return parent[x] = find(parent[x]);
}
void merge(int x, int y)
{
    x = find(x);
    y = find(y);
    if (x == y)
        return;
    if (parent[x] > parent[y])
        swap(x, y);
    parent[x] += parent[y];
    parent[y] = x;
}
bool related(int x, int y)
{
    return find(x) == find(y);
}
}
int main()
{
    ios::sync_with_stdio(false);
    cin >> n >> m >> s >> t;
    int a, b, c;
    for (int i = 0; i < m; i++)
    {
        cin >> a >> b >> c;
        e.push_back((edge){a, b, c});
    }
    sort(e.begin(), e.end());
    djs::init();
    int ans = 0;
    for (int i = 0; i < e.size() && !djs::related(s, t); i++)
    {
        djs::merge(e[i].from, e[i].to);
        ans = e[i].weight;
    }
    cout << ans << endl;
    return 0;
}