Codeforces 983E NN country 思维 （看题解）

#include<bits/stdc++.h>
#define LL long long
#define LD long double
#define ull unsigned long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ALL(x) (x).begin(), (x).end()
#define fio ios::sync_with_stdio(false); cin.tie(0);

using namespace std;

const int N = 2e5 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 998244353;
const double eps = 1e-8;
const double PI = acos(-1);

template<class T, class S> inline void add(T& a, S b) {a += b; if(a >= mod) a -= mod;}
template<class T, class S> inline void sub(T& a, S b) {a -= b; if(a < 0) a += mod;}
template<class T, class S> inline bool chkmax(T& a, S b) {return a < b ? a = b, true : false;}
template<class T, class S> inline bool chkmin(T& a, S b) {return a > b ? a = b, true : false;}

int n, m, q;
int in[N], ot[N], idx;
int pa[N][20], depth[N];
int go[N][20];
int ans[N];

vector<int> G[N];
vector<int> seg[N];
vector<PII> qus[N];

struct BIT {
    int a[N];
    void modify(int x, int v) {
        for(int i = x; i < N; i += i & -i) a[i] += v;
    }
    int sum(int x) {
        int ans = 0;
        for(int i = x; i; i -= i & -i) ans += a[i];
        return ans;
    }
    int query(int L, int R) {
        if(L > R) return 0;
        return sum(R) - sum(L - 1);
    }
} bit;

void dfs(int u, int fa) {
    depth[u] = depth[fa] + 1;
    pa[u][0] = fa;
    in[u] = ++idx;
    for(int i = 1; i < 20; i++)
        pa[u][i] = pa[pa[u][i - 1]][i - 1];
    for(auto &v : G[u]) {
        if(v == fa) continue;
        dfs(v, u);
    }
    ot[u] = idx;
}
int getLca(int u, int v) {
    if(depth[u] < depth[v]) swap(u, v);
    int dis = depth[u] - depth[v];
    for(int i = 19; i >= 0; i--)
        if(dis >> i & 1) u = pa[u][i];
    if(u == v) return u;
    for(int i = 19; i >= 0; i--)
        if(pa[u][i] != pa[v][i])
            u = pa[u][i], v = pa[v][i];
    return pa[u][0];
}

void dfs2(int u, int fa) {
    for(auto &v : G[u]) {
        if(v == fa) continue;
        dfs2(v, u);
        if(depth[go[v][0]] < depth[go[u][0]]) {
            go[u][0] = go[v][0];
        }
    }
}

void dfs3(int u, int fa) {
    vector<int> preVal(SZ(qus[u]));
    for(int i = 0; i < SZ(qus[u]); i++)
        preVal[i] = bit.query(in[qus[u][i].fi], ot[qus[u][i].fi]);
    for(auto &v : seg[u]) bit.modify(in[v], 1);
    for(auto &v : G[u]) {
        if(v == fa) continue;
        dfs3(v, u);
    }
    for(int i = 0; i < SZ(qus[u]); i++) {
        if(bit.query(in[qus[u][i].fi], ot[qus[u][i].fi]) == preVal[i]) ans[qus[u][i].se] += 2;
        else ans[qus[u][i].se]++;
    }
}

int main() {
    scanf("%d", &n);
    for(int i = 1; i <= n; i++) go[i][0] = i;
    for(int i = 2; i <= n; i++) {
        int fa; scanf("%d", &fa);
        G[fa].push_back(i);
    }
    dfs(1, 0);
    scanf("%d", &m);
    for(int i = 1; i <= m; i++) {
        int u, v;
        scanf("%d%d", &u, &v);
        int lca = getLca(u, v);
        if(depth[lca] < depth[go[u][0]]) go[u][0] = lca;
        if(depth[lca] < depth[go[v][0]]) go[v][0] = lca;
        seg[u].push_back(v);
        seg[v].push_back(u);
    }
    dfs2(1, 0);
    for(int j = 1; j < 20; j++)
        for(int i = 1; i <= n; i++)
            go[i][j] = go[go[i][j - 1]][j - 1];
    scanf("%d", &q);
    for(int o = 1; o <= q; o++){
        int u, v;
        scanf("%d%d", &u, &v);
        int lca = getLca(u, v);
        if(lca == u) {
            for(int i = 19; i >= 0; i--)
                if(depth[go[v][i]] > depth[lca])
                    v = go[v][i], ans[o] += 1 << i;
            if(depth[go[v][0]] > depth[lca]) ans[o] = -1;
            else ans[o]++;
        } else if(lca == v) {
            for(int i = 19; i >= 0; i--)
                if(depth[go[u][i]] > depth[lca])
                    u = go[u][i], ans[o] += 1 << i;
            if(depth[go[u][0]] > depth[lca]) ans[o] = -1;
            else ans[o]++;
        } else {
            for(int i = 19; i >= 0; i--)
                if(depth[go[v][i]] > depth[lca])
                    v = go[v][i], ans[o] += 1 << i;
            for(int i = 19; i >= 0; i--) {
                if(depth[go[u][i]] > depth[lca]) {
                    u = go[u][i], ans[o] += 1 << i;
                }
            }
            if(depth[go[u][0]] > depth[lca] || depth[go[v][0]] > depth[lca]) ans[o] = -1;
            else qus[u].push_back(mk(v, o));
        }
    }
    dfs3(1, 0);
    for(int i = 1; i <= q; i++) printf("%d\n", ans[i]);
    return 0;
}

/*
*/