[POJ3728]The merchant（tanrjan_lca + DP）

传送门

比着题解写还错。。。

查了两个小时没查出来，心态爆炸啊

以后再查

——代码（WA）

 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #define N 2000001
 #define Min(x, y) ((x) < (y) ? (x) : (y))
 #define Max(x, y) ((x) > (y) ? (x) : (y))
 #define swap(x, y) ((x) ^= (y) ^= (x) ^= (y))

 int n, m, cnt, qcnt, acnt;
 int f[N], fa[N], max[N], min[N], up[N], down[N], ans[N];
 int head[N], to[N << ], next[N << ], qhead[N], qu[N << ], qv[N << ], qid[N << ], qnext[N << ], ahead[N], ato[N << ], anext[N << ];

 inline int read()
 {
     int x = , f = ;
     char ch = getchar();
     for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -;
     for(; isdigit(ch); ch = getchar()) x = (x << ) + (x << ) + ch - '';
     return x * f;
 }

 inline void add(int x, int y)
 {
     to[cnt] = y;
     next[cnt] = head[x];
     head[x] = cnt++;
 }

 inline void add_ask(int x, int y, int z)
 {
     qu[qcnt] = x;
     qv[qcnt] = y;
     qid[qcnt] = z;
     qnext[qcnt] = qhead[x];
     qhead[x] = qcnt++;
 }

 inline void add_ans(int x, int y)
 {
     ato[acnt] = y;
     anext[acnt] = ahead[x];
     ahead[x] = acnt++;
 }

 inline int find(int x)
 {
     if(x ^ f[x])
     {
         int fx = f[x];
         f[x] = find(f[x]);
         up[x] = Max(up[x], Max(up[fx], max[fx] - min[x]));
         down[x] = Max(down[x], Max(down[fx], max[x] - min[fx]));
         max[x] = Max(max[fx], max[x]);
         min[x] = Min(min[fx], max[x]);
     }
     return f[x];
 }

 inline void dfs(int u)
 {
     int i, v, x, y;
     f[u] = u;
     for(i = qhead[u]; i ^ -; i = qnext[i])
         if(f[qv[i]])
         {
             x = find(qv[i]);
             add_ans(x, i);
         }
     for(i = head[u]; i ^ -; i = next[i])
     {
         v = to[i];
         if(v ^ fa[u]) fa[v] = u, dfs(v);
     }
     for(i = ahead[u]; i ^ -; i = anext[i])
     {
         x = qu[ato[i]];
         y = qv[ato[i]];
         find(x), find(y);
         if(ato[i] & ) swap(x, y);
         ans[qid[ato[i]]] = Max(max[y] - min[x], Max(up[x], down[y]));
     }
     f[u] = fa[u];
 }

 int main()
 {
     int i, j, x, y;
     while(~scanf("%d", &n))
     {
         cnt = qcnt = acnt = ;
         memset(head, -, sizeof(head));
         memset(qhead, -, sizeof(qhead));
         memset(ahead, -, sizeof(ahead));
         memset(f, , sizeof(f));
         memset(fa, , sizeof(fa));
         memset(ans, , sizeof(ans));
         for(i = ; i <= n; i++) min[i] = max[i] = read(), up[i] = down[i] = ;
         for(i = ; i < n; i++)
         {
             x = read();
             y = read();
             add(x, y);
             add(y, x);
         }
         m = read();
         for(i = ; i <= m; i++)
         {
             x = read();
             y = read();
             add_ask(x, y, i);
             add_ask(y, x, i);
         }
         dfs();
         for(i = ; i <= m; i++) printf("%d\n", ans[i]);
     }
     return ;
 }