给出一颗以1为根的树,一开始每个节点都是一颗棋子,一面白一面黑,白色的面朝上
接下来就q次操作,操作分两种
0操作 将一个颗棋子翻转
1操作 询问一颗棋子与所有面朝上为黑色的棋子lca最深的那个的编号
LCA(最近公共祖先) + DFS序
不早了先不发详细题解
开氧气才能过,能优化的都优化了,还是T,75分,开了就A了
看:
#pragma GCC optimize(2)
#include
#include
#include
#define rgi register int
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin)),p1==p2?EOF:*p1++)
using namespace std;
const int N = 800010;
int n, q, tot, cnt;
int dfn[N], id[N], f[N][24], dep[N], next[N], to[N], last[N], siz[N], que[N];
set <int> S;
set <int>::iterator it;
char buf[1 << 21], *p1, *p2;
inline int in() {
int f = 0, flag = 1; char c = getchar();
while(!isdigit(c)) {if(c == '-') flag = -1; c = getchar();}
while(isdigit(c)) f = (f << 3) + (f << 1) + c - 48, c = getchar();
return f * flag;
}
int LCA(int x,int y) {
if(dep[x] < dep[y]) swap(x, y);
rgi need = dep[x] - dep[y];
for(rgi i = 0; need; need >>= 1, ++i) if(need & 1) x = f[x][i];
if(x != y) {
for (rgi i = 21; i >= 0; i--) if(f[x][i] != f[y][i])
x = f[x][i], y = f[y][i];
return f[x][0];
}
return x;
}
void bfs_() {
rgi h = 0, t = 1, u, v;
que[++h] = 1;
while(h <= t) {
u = que[h++];
siz[u] = 1;
for (rgi i = last[u]; i; i = next[i]) {
v = to[i];
dep[v] = dep[u]+1, f[v][0] = u;
que[++t] = v;
}
}
for (rgi i = n; i >= 1; i--) siz[f[que[i]][0]]+=siz[que[i]];
}
void bfs__() {
rgi h = 0, t = 1, u, v, Last;
que[++h] = dfn[1] = id[1] = 1;
while(h <= t) {
u = que[h++], Last = u;
for (rgi i = last[u]; i; i = next[i]) {
v = to[i];
dfn[v] = dfn[Last] + (Last !=u ? siz[Last] : 1);
id[dfn[v]] = v;
que[++t] = v;
Last = v;
}
}
}
void Init() {
n = in(), q = in();
rgi fa;
for (rgi i = 2; i <= n; ++i)
{ fa = in(), to[++cnt] = i, next[cnt] = last[fa], last[fa] = cnt; }
bfs_(), bfs__(); dep[0] = -1;
for (rgi j = 1; (1 << j) <= n; ++j)
for (rgi i = 1; i <= n; ++i)
if (f[i][j - 1]) f[i][j] = f[f[i][j - 1]][j - 1];
}
void print(int x) {
if (x > 9) print(x / 10); putchar(x % 10 + 48); return;
}
void Main() {
rgi flag, t, T, F;
for (rgi i = 1; i <= q; ++i) {
flag = in(), F = 0;
if (flag < 0) F = 1, flag = -flag;
if (!F) {
if (!S.insert(dfn[flag]).second)
S.erase(dfn[flag]);
continue;
}
if (S.empty()) { putchar(48), putchar('\n'); continue;}
t = 0, T = 0;
it = S.lower_bound(dfn[flag]);
if (it != S.end()) t = LCA(flag, id[*it]);
if (it != S.begin()) it--, T = LCA(flag, id[* it]);
print(dep[t] < dep[T] ? T : t); putchar('\n');
}
}
int main() {
/*freopen("watch.in","r",stdin);
freopen("watch.out","w",stdout);*/
Init();
Main();
return 0;
}