HihoCoder - 1121 二分图判定

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 1e5 + 10;
const int maxm = 4 * 1e5 + 10;
int tot;
int head[maxn];
int vis[maxn];
struct Edge {
    int to, next;
}edge[maxm<<1];

void init(int n) {
    tot = 0;
    for (int i = 0; i <= n; i++) head[i] = -1, vis[i] = 0;
}

void addedge(int u, int v) {
    tot++;
    edge[tot].to = v;
    edge[tot].next = head[u];
    head[u] = tot;
}
bool dfs(int u) {
    for (int i = head[u]; i != -1; i = edge[i].next) {
        int v = edge[i].to;
        if (vis[v]) {
            if (vis[v] == -vis[u]) continue;
            else return false;
        }
        else {
            vis[v] = -vis[u];
            if (!dfs(v)) return false;
        }
    }
    return true;
}
int main() {
    int T; scanf("%d", &T);
    for (int kase = 1; kase <= T; kase++) {
        int n, m; scanf("%d %d", &n, &m);
        init(n);
        for (int i = 1; i <= m; i++) {
            int u, v; scanf("%d %d", &u, &v);
            addedge(u, v); addedge(v, u);
        }
        bool ok = true;
        for (int i = 1; i <= n; i++) {
            if (!vis[i]) {
                vis[i] = 1;
                if (!dfs(i)) { ok = false; break; }
            }
        }
        if (ok) printf("Correct\n");
        else printf("Wrong\n");
    }
}