HDU2665（可持久化线段树板子）

1.题意有坑，实际要求第k小。

2.没学过动态开点也没学过主席树，看一下博主思路然后妄想自己实现的后果就是拿命去调bug。

const int maxn = 1e5 + 5;
int test, n, m, tot;
int a[maxn], b[maxn];

namespace Seg {
    #define ls(p) t[p].l
    #define rs(p) t[p].r

    int sz, root[maxn];
    struct Node {
        int sum, l, r;
    }t[maxn * 20];

    int Build(int l, int r) {
        int p = ++sz;
        if (l == r) {
            t[p].sum = t[p].l = t[p].r = 0;
            return sz;
        }
        int mid = (l + r) >> 1;
        t[p].l = Build(l, mid);
        t[p].r = Build(mid + 1, r);
        t[p].sum = t[ls(p)].sum + t[rs(p)].sum;
        return p;
    }

    int Update(int l, int r, int last, int k) {
        int p = ++sz;
        t[p].l = t[last].l, t[p].r = t[last].r, t[p].sum = 0;
        if (l == r) {
            t[p].sum = t[last].sum + 1;
            return p;
        }
        int mid = (l + r) >> 1;
        if (k <= mid)   t[p].l = Update(l, mid, ls(last), k);
        else    t[p].r = Update(mid + 1, r, rs(last), k);
        t[p].sum = t[ls(p)].sum + t[rs(p)].sum;
        return p;
    }

    int Query(int l, int r, int last, int p, int k) {
        if (l == r) return b[l];
        int res = t[ls(p)].sum - t[ls(last)].sum;
        int mid = (l + r) >> 1;
        if (res >= k)    return Query(l, mid, ls(last), ls(p), k);
        else    return Query(mid + 1, r, rs(last), rs(p), k - res);
    }
};

int main() {
    for (read(test); test--; ) {
        read(n), read(m);
        rep(i, 1, n)    read(a[i]), b[i] = a[i];
        sort(b + 1, b + 1 + n);
        tot = unique(b + 1, b + 1 + n) - b - 1;
        rep(i, 1, n)    a[i] = lower_bound(b + 1, b + 1 + tot, a[i]) - b;

        Seg::sz = 0;
        Seg::root[0] = Seg::Build(1, tot);
        rep(i, 1, n)    Seg::root[i] = Seg::Update(1, tot, Seg::root[i - 1], a[i]);
        while (m--) {
            int l, r, k;
            read(l), read(r), read(k);
            writeln(Seg::Query(1, tot, Seg::root[l - 1], Seg::root[r], k));
        }
    }
    return 0;
}