[JZOJ 5782] 城市猎人

Posted 2021-01-03 akoasm

思路：
并查集按秩合并维护出现时间。
最早连接时间就是树上连接最大值。
(qwq)我居然把路径压缩和按秩合并打到一个程序里了...OvO

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1000010;
struct edge {
    int to;
    int nxt;
    int w;
}e[maxn << 1];

//struct asks{
//  int x,y;
//}q[maxn<<1];

int n,m,q,cnt;
int x,y;
int rank[maxn];
int fa[maxn];
int head[maxn];

inline int find(int x) {
    return x == fa[x] ? x : find(fa[x]);
} 


inline void Add_edge(int u,int v,int w) {
    e[++cnt].w = w;
    if(rank[u] > rank[v]) {
        fa[v] = u;
        e[cnt].to = u;
        e[cnt].nxt = head[v];
        head[v] = cnt;
    }
    else {
        fa[u] = v;
        e[cnt].to = v;
        e[cnt].nxt = head[u];
        head[u] = cnt;
        if(rank[u] == rank[v]) rank[u] ++;
    }
    return;
}

inline int query(int x,int y) {
    int dx = 0;
    int dy = 0;
    int res = 0;
    int l = x;
    int r = y;
    while(fa[l] != l) {
        l = fa[l];
        dx++;
    }
    while(fa[r] != r) {
        r = fa[r];
        dy ++;
    }
    if(dx < dy) {
        swap(dx,dy);
        swap(x,y);
    }
    while(dx > dy) {
        res = max(e[head[x]].w,res);
        x = fa[x];
        dx --;
    }
    if(x == y) return res;
    while(x != y) {
        res = max(res,max(e[head[x]].w,e[head[y]].w));
        x = fa[x];y = fa[y];
    }
    return res;
}

int main () {
    #ifdef ONLINE_JUDGE
        freopen("pictionary.in","r",stdin);
        freopen("pictionary.out","w",stdout);
    #endif
    scanf("%d %d %d",&n,&m,&q);
    for(int i = 1;i <= n; ++i) {
        fa[i] = i;
    }
    for(int i = 1;i <= m; ++i){
        int d = m - i + 1;
        for(int j = d*2;j <= n;j += d) {
            Add_edge(find(d),find(j),i);
            //cout<<d << ‘ ‘<< j<<endl;
        }
    }
    for(int i = 1;i <= q; ++i) {
        scanf("%d %d",&x,&y);
        printf("%d
",query(x,y));
    }
    return 0;
    
}