POJ 2104 K-th Number（划分树）

#include <stdio.h>
#include <string.h>
#include <algorithm>
using namespace std;

const int N = 100007;

int n, m;
int sorted[N], tree[20][N], toleft[20][N];

void build(int L, int R, int dep)
{
    if (L == R)
        return;
    int mid = (L + R) >> 1, same = mid - L + 1, lpos = L, rpos = mid + 1;
    for (int i = L; i <= mid; i++)
    {
        if (tree[dep][i] < sorted[mid])
            same--;
    }
    for (int i = L; i <= R; i++)
    {
        if (tree[dep][i] < sorted[mid])
            tree[dep+1][lpos++] = tree[dep][i];
        else if (tree[dep][i] == sorted[mid] && same > 0)
        {
            tree[dep+1][lpos++] = tree[dep][i];
            same--;
        }
        else
            tree[dep+1][rpos++] = tree[dep][i];
        toleft[dep][i] = lpos - L;
    }
    build(L, mid, dep + 1);
    build(mid + 1, R, dep + 1);
}

int query(int L, int R, int l, int r, int k, int dep)
{
    if (l == r)
        return tree[dep][l];
    int mid = (L + R) >> 1, temp = toleft[dep][l-1];
    if (l == L)
        temp = 0;
    int cnt = toleft[dep][r] - temp, newl, newr;
    if (cnt >= k)
    {
        newl = L + temp;
        newr = newl + cnt - 1;
        return query(L, mid, newl, newr, k, dep + 1);
    }
    else
    {
        newl = mid + 1 + l - L - temp;
        newr = mid + 1 + r - L - toleft[dep][r];
        return query(mid + 1, R, newl, newr, k - cnt, dep + 1);
    }
}

int main()
{
    while (scanf("%d%d", &n, &m) != EOF)
    {
        for (int i = 1; i <= n; i++)
        {
            scanf("%d", &sorted[i]);
            tree[0][i] = sorted[i];
        }
        sort(sorted + 1, sorted + 1 + n);
        build(1, n, 0);
        for (int i = 0; i < m; i++)
        {
            int l, r, k;
            scanf("%d%d%d", &l, &r, &k);
            printf("%d\n", query(1, n, l, r, k, 0));
        }
    }
    return 0;
}