求调，A #1，其他都 WA

代码：

#define genshin
#include <bits/stdc++.h>

using namespace std;

#define int long long

#define fir first
#define sec second
#define lep( i, l, r ) for ( int i = ( l ); i <= ( r ); i ++ )
#define rep( i, r, l ) for ( int i = ( r ); i >= ( l ); i -- )
#define gep( i, x ) for ( int i = head[( x )]; i; i = edges[i].next)

char _c; bool _f; template < class T > inline void read ( T &x ) {
    _f = 0, x = 0;
    while ( _c = getchar (), !isdigit (_c) ){
        if ( _c == '-' ) { _f = 1; }
    }
    while ( isdigit (_c) ){
        x = x * 10 + _c - '0', _c = getchar ();
        if (_f) { x = -x; }
    }
}

const int N = 3e5 + 5;
const int INF = 1145141919810;

int n;
int a[N], p[N];

int head[N], tot;

struct Graph {
  int to, w, id, next;
} edges[N << 1];

void add ( int u, int v, int w, int id ) {
  tot ++;
  edges[tot].to = v;
  edges[tot].w = w;
  edges[tot].id = id;
  edges[tot].next = head[u];
  head[u] = tot;
}

int tree[N << 2], tag[N << 2];

void pushup ( int node ) {
  tree[node] = max ( tree[node << 1], tree[node << 1 | 1] );
}

void update ( int node, int lt, int rt, int x, int k ) {
  if ( x < lt || x > rt ) {
    return ;
  }
  if ( lt == rt && lt == x ) {
    tree[node] = k;
    // cout << "segment: " << k << '\n';
    return ;
  }
  int mid = lt + rt >> 1;
  update ( node << 1, lt, mid, x, k ), update ( node << 1 | 1, mid + 1, rt, x, k );
  pushup ( node );
}

int query ( int node, int lt, int rt, int x, int y ) {
  if ( y < lt || x > rt ) {
    return -INF;
  }
  if ( x <= lt && rt <= y ) {
    return tree[node];
  }
  int mid = lt + rt >> 1;
  return max ( query ( node << 1, lt, mid, x, y ), query ( node << 1 | 1, mid + 1, rt, x, y ) );
}

void dfs ( int x, int fa ) {
  for ( int i = head[x]; i; i = edges[i].next ) {
    if ( edges[i].to != fa ) {
      dfs ( edges[i].to, x );
      a[edges[i].to] = edges[i].w;
      p[edges[i].id] = edges[i].to;
    }
  }
}

int cnt;
int dad[N], siz[N], top[N], dep[N], son[N], dfn[N];

void dfs1 ( int x, int fa ) {
  dfn[x] = ++ cnt;
  dad[x] = fa;
  siz[x] = 1;
  dep[x] = dep[fa] + 1;
  int maxi = -INF;
  for ( int i = head[x]; i; i = edges[i].next ) {
    if ( edges[i].to != fa ) {
      dfs1 ( edges[i].to, x );
      siz[x] += siz[edges[i].to];
      if ( siz[edges[i].to] > maxi ) {
        maxi = siz[edges[i].to];
        son[x] = edges[i].to;
      }
    }
  }
}

void dfs2 ( int x, int t ) {
  top[x] = t;
  update ( 1, 1, n, dfn[x], a[x] );
  if ( !son[x] ) {
    return ;
  }
  dfs2 ( son[x], t );
  for ( int i = head[x]; i; i = edges[i].next ) {
    if ( edges[i].to != dad[x] && edges[i].to != son[x] ) {
      dfs2 ( edges[i].to, edges[i].to );
    }
  }
}

int ask ( int x, int y ) {
  int ans = -INF;
  while ( top[x] != top[y] ) {
    if ( dep[top[x]] < dep[top[y]] ) {
      swap ( x, y );
    }
    ans = max ( ans, query ( 1, 1, n, dfn[top[x]], dfn[x] ) );
    x = dad[top[x]];
  }
  if ( dep[x] > dep[y] ) {
    swap ( x, y );
  }
  ans = max ( ans, query ( 1, 1, n, dfn[x], dfn[y] ) );
  return ans;
}

int lca ( int x, int y ) {
  while ( top[x] != top[y] ) {
    if ( dep[top[x]] < dep[top[y]] ) {
      swap ( x, y );
    }
    x = dad[top[x]];
  }
  if ( dep[x] > dep[y] ) {
    swap ( x, y );
  }
  return x;
}

void Solve () {
  cin >> n;
  for ( int i = 1; i < n; i ++ ) {
    int u, v, w;
    cin >> u >> v >> w;
    add ( u, v, w, i ), add ( v, u, w, i );
  }
  dfs ( 1, 0 );
  dfs1 ( 1, 0 );
  dfs2 ( 1, 1 );
  string op;
  while ( cin >> op ) {
    if ( op == "CHANGE" ) {
      int x, t;
      cin >> x >> t;
      update ( 1, 1, n, dfn[p[x]], t );
      // cout << "change: " << dfn[p[x]] << '\n';
    }
    else if ( op == "QUERY" ) {
      int a, b;
      cin >> a >> b;
      int tmp = lca ( a, b ), tmp2 = query ( 1, 1, n, dfn[tmp], dfn[tmp] );
      update ( 1, 1, n, dfn[tmp], -INF );
      cout << ask ( a, b ) << '\n';
      update ( 1, 1, n, dfn[tmp], tmp2 );
    }
    else {
      break;
    }
    // for ( int i = 1; i <= n; i ++ ) {
    //   cout << query ( 1, 1, n, dfn[i], dfn[i] ) << " ";
    // }
    // cout << '\n';
  }
}

signed main () {
#ifdef genshin
  freopen ( "test.in", "r", stdin );
  freopen ( "test.out", "w", stdout );
#endif
  Solve ();
    return 0;
}

感觉代码还算清晰把吧。