bzoj1854【二分圖】

第一次做的時候居然沒看出來二分圖。。

一直想數據結構。。。

中毒太深。。

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;
int n;
 
struct edge {
    int v,next;
}e[4000010];
int cnt,head[1010010];
 
int Link[1010010],vis[1010010];
 
int read_int () {
    char c = getchar();
    int re = 0;
    for(;c > '9' || c < '0';c = getchar());
    for(;c >= '0' && c <= '9';c = getchar())
        re = re * 10 + c - '0';
    return re;
}
 
void adde (int u,int v) {
    e[++cnt].v = v;
    e[cnt].next = head[u];
    head[u] = cnt;
    e[++cnt].v = u;
    e[cnt].next = head[v];
    head[v] = cnt;
}
 
bool find (int u,int f) {
    for(int i = head[u];i != -1;i = e[i].next) {
        int v = e[i].v;
        if(vis[v] == f)
            continue;
        vis[v] = f;
        if(!Link[v] || find(Link[v],f)) {
            Link[v] = u;
            Link[u] = v;
            return 1;
        }
    }
    return 0;
}
 
int main () {
    memset(head,-1,sizeof head);
    n = read_int();
     
    int upp = 0;
    for(int i = 1;i <= n;++i) {
        int t1 = read_int();
        int t2 = read_int();
        upp = max(upp,t1);
        upp = max(upp,t2);
        adde(t1 + n,i);
        adde(t2 + n,i);
    }
     
    for(int i = 1;i <= upp;++i) {
        if(Link[n + i])
            continue;
        vis[n + i] = i;
        if(!find(n + i,i)) {
            printf("%d\n",i - 1);
            return 0;
        }
    }
    printf("%d\n",upp);
}