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| #include <algorithm> #include <cstdio> #include <cstring> #include <iostream> #include <vector> using namespace std;
const int MAXN = 100010; const int INF = 0x3f3f3f3f;
class LFS { public: LFS() { memset(head, -1, sizeof head); ecnt = 0; n = 0; } LFS(int N) { memset(head, -1, sizeof head); ecnt = 0; n = N; } void adde(int from, int to, int w) { e[ecnt].to = to; e[ecnt].w = w; e[ecnt].next = head[from]; head[from] = ecnt++; } void addde(int a, int b, int w) { adde(a, b, w); adde(b, a, w); }
protected: struct Edge { int to, next, w; } e[MAXN * 2]; int head[MAXN]; int ecnt; int n;
private: virtual void dfs(int u, int fa) { for (int i = head[u]; i != -1; i = e[i].next) { int v = e[i].to; if (v != fa) { dfs(v, u); } } } };
class LCA : public LFS{ public: int dep[MAXN]; LCA(int n) : LFS(n) { memset(dep, -1, sizeof dep); } void pre(int rt = 1) { dfs(rt, 1, 0); } int querylca(int a, int b) { if (dep[a] > dep[b]) swap(a, b); int h = dep[b] - dep[a]; for (int i = 20; i >= 0; i--) { if(h & (1 << i)) { b = f[b][i]; } } if (a == b) return a; for (int i = 20; i >= 0; i--) { if (f[a][i] == f[b][i]) continue; a = f[a][i]; b = f[b][i]; } return f[a][0]; } int querydis(int a,int b){ int lca = querylca(a,b); return dep[a] + dep[b] - dep[lca]*2; }
protected: int f[MAXN][22];
private: void dfs(int u, int d, int fa) { dep[u] = d; f[u][0] = fa; for (int i = 1; i < 21; i++) { f[u][i] = f[f[u][i - 1]][i - 1]; } for (int i = head[u]; i != -1; i = e[i].next) { int v = e[i].to; if (dep[v] == -1) { dfs(v, d + 1, u); } } } };
#include <cctype> #include <cstdio>
inline int read() { int X = 0, w = 0; char ch = 0; while (!isdigit(ch)) { w |= ch == '-'; ch = getchar(); } while (isdigit(ch)) { X = (X << 3) + (X << 1) + (ch ^ 48); ch = getchar(); } return w ? -X : X; }
int solve(LCA* tree,int a,int b,int c){ int disab = tree->querydis(a,b); int disac = tree->querydis(a,c); int disbc = tree->querydis(b,c); return (disab + disac - disbc) / 2 + 1; }
int main(){ int n,q; cin >> n >> q; LCA* tree = new LCA(n); for(int i = 2;i<=n;i++){ int a; cin >> a; tree->addde(i,a,1); } tree->pre(); for(int i = 1;i<=q;i++){ int a,b,c; cin >> a >> b >> c; int ans = 0; ans = max(solve(tree,a,b,c),max(solve(tree,b,a,c),solve(tree,c,a,b))); cout << ans << endl; } }
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