重量差異

10.11

思路：
加權並查集的經典應用。每個點儲存它與根節點的重量差，合併與路徑壓縮時維護一下就好。
離線的按秩合併可能會T掉。。。

#include <cstdio>
#define LL long long
#define N 200010

int n, m;
int fa[N];
LL r[N];
char ss[210];

int getfather(int x){
    if(x == fa[x]) return x;
    int tmp = getfather(fa[x]);
    r[x] += r[fa[x]];//壓縮時維護權值 
    return
 
 fa[x] = tmp;
}

int main(){
    freopen("b.in", "r", stdin);
    freopen("b.out", "w", stdout);
    scanf("%d%d", &n, &m);
    for(int i=1; i<=n; i++) fa[i] = i;
    while( m-- ){
        int u, v, w;
        scanf("%s", ss);
        if(ss[0] == '!'){
            scanf("%d%d%d", &u, &v, &w);
            int
 
 x = getfather(u), y = getfather(v);
            if(x != y)
                fa[x] = fa[y], r[x] = w + r[v] - r[u];
        }
        else{
            scanf("%d%d", &u, &v);
            int x = getfather(u), y = getfather(v);
            if(x != y) printf("UNKNOWN\n");
            else printf
 
("%I64d\n", r[u]-r[v]);
        }
    }
    return 0;
}