RMQ

ST表

void build () {
    for (int i = 1; i <= n; i++) f[i][0] = a[i];
    for (int len = 1; (1 << len) <= n; len++) {
        for (int l = 1; l + (1 << len) - 1 <= n; l++) {
            f[l][len] = Max (f[l][len - 1], f[l + (1 << len - 1)][len - 1]);
        }
    }
}

int RMQ (int l, int r) {
    int k = log (r - l + 1) / log (2);
    return Max (f[l][k], f[r - (1 << k) + 1][k]);
}