树剖板子题。
维护区间最大值。
1 #include<cstdio> 2 #include<iostream> 3 #include<cmath> 4 #include<algorithm> 5 #include<cstring> 6 #include<cstdlib> 7 #include<cctype> 8 #include<vector> 9 #include<stack> 10 #include<queue> 11 using namespace std; 12 #define enter puts("") 13 #define space putchar(' ') 14 #define Mem(a, x) memset(a, x, sizeof(a)) 15 #define rg register 16 typedef long long ll; 17 typedef double db; 18 const int INF = 0x3f3f3f3f; 19 const db eps = 1e-8; 20 const int maxn = 1e5 + 5; 21 inline ll read() 22 { 23 ll ans = 0; 24 char ch = getchar(), last = ' '; 25 while(!isdigit(ch)) last = ch, ch = getchar(); 26 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar(); 27 if(last == '-') ans = -ans; 28 return ans; 29 } 30 inline void write(ll x) 31 { 32 if(x < 0) x = -x, putchar('-'); 33 if(x >= 10) write(x / 10); 34 putchar(x % 10 + '0'); 35 } 36 37 int n, q; 38 char c[2]; 39 40 struct Edge 41 { 42 int nxt, to; 43 }e[maxn << 1]; 44 int head[maxn], ecnt = -1; 45 void addEdge(int x, int y) 46 { 47 e[++ecnt] = (Edge){head[x], y}; 48 head[x] = ecnt; 49 } 50 51 int dep[maxn], fa[maxn], siz[maxn], son[maxn]; 52 void dfs1(int now, int _f) 53 { 54 siz[now] = 1; 55 for(int i = head[now], v; i != -1; i = e[i].nxt) 56 { 57 v = e[i].to; 58 if(v == _f) continue; 59 dep[v] = dep[now] + 1; 60 fa[v] = now; 61 dfs1(v, now); 62 siz[now] += siz[v]; 63 if(!son[now] || siz[son[now]] < siz[v]) son[now] = v; 64 } 65 } 66 int dfsx[maxn], pos[maxn], top[maxn], cnt = 0; 67 void dfs2(int now, int _f) 68 { 69 dfsx[now] = ++cnt; pos[cnt] = now; 70 if(son[now]) top[son[now]] = top[now], dfs2(son[now], now); 71 for(int i = head[now], v; i != -1; i = e[i].nxt) 72 { 73 v = e[i].to; 74 if(v == son[now] || v == _f) continue; 75 top[v] = v; 76 dfs2(v, now); 77 } 78 79 } 80 81 bool vis[maxn]; 82 int l[maxn << 2], r[maxn << 2], dat[maxn << 2]; 83 void build(int L, int R, int now) 84 { 85 l[now] = L; r[now] = R; 86 if(L == R) return; 87 int mid = (L + R) >> 1; 88 build(L, mid, now << 1); 89 build(mid + 1, R, now << 1 | 1); 90 } 91 void update(int idx, int now) 92 { 93 if(l[now] == r[now]) {dat[now] = idx; return;} 94 int mid = (l[now] + r[now]) >> 1; 95 if(idx <= mid) update(idx, now << 1); 96 else update(idx, now << 1 | 1); 97 dat[now] = max(dat[now << 1], dat[now << 1 | 1]); 98 } 99 int query(int L, int R, int now) 100 { 101 if(!dat[now]) return -INF; 102 if(l[now] == L && r[now] == R) return dat[now]; 103 int mid = (l[now] + r[now]) >> 1; 104 if(R <= mid) return query(L, R, now << 1); 105 else if(L > mid) return query(L, R, now << 1 | 1); 106 else return max(query(L, mid, now << 1), query(mid + 1, R, now << 1 | 1)); 107 } 108 109 int query_path(int x) 110 { 111 int ret = -INF; 112 while(top[x] != 1) 113 { 114 ret = max(ret, query(dfsx[top[x]], dfsx[x], 1)); 115 x = fa[top[x]]; 116 } 117 ret = max(ret, query(1, dfsx[x], 1)); 118 return pos[ret]; 119 } 120 121 int main() 122 { 123 Mem(head, -1); 124 n = read(); q = read(); 125 for(int i = 1; i < n; ++i) 126 { 127 int x = read(), y = read(); 128 addEdge(x, y); addEdge(y, x); 129 } 130 dfs1(1, 0); top[1] = 1; dfs2(1, 0); 131 build(1, cnt, 1); 132 update(dfsx[1], 1); vis[1] = 1; 133 for(int i = 1; i <= q; ++i) 134 { 135 scanf("%s", c); int x = read(); 136 if(c[0] == 'C') 137 { 138 if(!vis[x]) update(dfsx[x], 1), vis[x] = 1; 139 } 140 else write(query_path(x)), enter; 141 } 142 return 0; 143 }