「PKUSC2018」星际穿越

传送门

Solution 

倍增

Code 

#include <bits/stdc++.h>
#define reg register
#define ll long long

using namespace std;

int read() {
    int x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-')
            f = -1;
        ch = getchar();
    }
    while (ch <= '9' && ch >= '0') {
        x = (x << 1) + (x << 3) + ch - '0';
        ch = getchar();
    }
    return x * f;
}

const int MN = 3e5 + 5;

int gcd(int x, int y) { return !y ? x : gcd(y, x % y); }

int N, l[MN];
int p[MN][20], v[MN][20];

int cal(int L, int x) {
    if (L == x)
        return 0;
    if (L >= l[x])
        return x - L;
    int r = x - L, step = 0, i;
    for (x = l[x], i = 18; ~i; --i)
        if (p[x][i] >= L) {
            r += v[x][i] + (x - p[x][i]) * step;
            step += 1 << i;
            x = p[x][i];
        }
    r += (x - L) * (step + 1);
    return r;
}

int main() {
    N = read();
    reg int i, j;
    for (l[1] = 0, i = 2; i <= N; ++i) l[i] = read();
    for (p[N][0] = l[N], i = N - 1; i; --i) p[i][0] = min(l[i], p[i + 1][0]);
    for (j = 1; j <= 18; ++j)
        for (i = 1; i <= N; ++i)
            if (p[i][j - 1])
                p[i][j] = p[p[i][j - 1]][j - 1];

    for (i = 1; i <= N; ++i) v[i][0] = i - p[i][0];
    for (j = 1; j <= 18; ++j)
        for (i = 1; i <= N; ++i)
            if (p[i][j])
                v[i][j] = v[i][j - 1] + v[p[i][j - 1]][j - 1] + (p[i][j - 1] - p[i][j]) * (1 << (j - 1));

    int Q = read(), L, R, x;
    while (Q--) {
        L = read(), R = read(), x = read();
        int P = cal(L, x) - cal(R + 1, x), q = R - L + 1;
        int g = gcd(P, q);
        printf("%d/%d\n", P / g, q / g);
    }
    return 0;
}

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