洛谷 P1525 关押罪犯

传送门

同 AcWing 257 关押罪犯

#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using p = pair<int, int>;
const int maxn(2e4 + 10);
const int maxm(2e5 + 10);
int ecnt, head[maxn];
int color[maxn];    // 0: 未染色; 1: 染白色; 2: 染黑色

struct edge {
    int to, wt, nxt;
} edges[maxm];

template<typename T = int>
inline const T read()
{
    T x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-') f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = (x << 3) + (x << 1) + ch - '0';
        ch = getchar();
    }
    return x * f;
}

template<typename T>
inline void write(T x, bool ln)
{
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    if (x > 9) write(x / 10, false);
    putchar(x % 10 + '0');
    if (ln) putchar(10);
}

void addEdge(int u, int v, int w)
{
    edges[ecnt].to = v;
    edges[ecnt].wt = w;
    edges[ecnt].nxt = head[u];
    head[u] = ecnt++;
}

bool dfs(int u, int c, int val)
{
    color[u] = c;
    for (int i = head[u]; compl i; i = edges[i].nxt) {
        int v = edges[i].to, w = edges[i].wt;
        if (w <= val) {
            continue;
        }
        if (color[v] == c) {
            return false;
        } else if (not color[v] and not dfs(v, 3 - c, val)) {
            return false;
        }
    }
    return true;
}

bool judge(int n, int val)
{
    memset(color, 0, sizeof color);
    for (int i = 1; i <= n; ++i) {
        if (not color[i] and not dfs(i, 1, val)) {
            return false;
        }
    }
    return true;
}

int main()
{
#ifdef ONLINE_JUDGE
#else
    freopen("input.txt", "r", stdin);
#endif
    ios::sync_with_stdio(false);
    memset(head, -1, sizeof head);
    int n = read(), m = read();
    while (m--) {
        int u = read(), v = read(), w = read();
        addEdge(u, v, w);
        addEdge(v, u, w);
    }
    int low = 0, high = 1e9;
    while (low < high) {
        int mid = (low + high) / 2;
        if (judge(n, mid)) {
            high = mid;
        } else {
            low = mid + 1;
        }
    }
    write(low, true);
    return 0;
}