HDU_2665_劃分樹

題意：給你一個n個數的序列，有m個詢問，對於每個詢問a, b, k的意思是在區間a, b內第k大的數是什麼，劃分樹水題，貼代碼：

劃分樹講解：HERE

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>

using namespace std;

const int N = 100000 + 10;

int sorted[N], val[30][N], tlsum[30][N];

void build(int l, int r, int d)
{
    if(l == r)  return ;

    int mid = (l + r) >> 1;
    int same = mid - l + 1;

    for(int i=l; i<=r; ++i)
        if(val[d][i] < sorted[mid])
            --same;
    int lp = l, rp = mid + 1;
    for(int i=l; i<=r; ++i)
    {
        if(i == l)  tlsum[d][i] = 0;
        else        tlsum[d][i] = tlsum[d][i-1];

        if(val[d][i] < sorted[mid])
        {
            ++tlsum[d][i];
            val[d+1][lp++] = val[d][i];
        }
        else if(val[d][i] > sorted[mid])
            val[d+1][rp++] = val[d][i];
        else
        {
            if(same)
            {
                --same;
                ++tlsum[d][i];
                val[d+1][lp++] = val[d][i];
            }
            else
                val[d+1][rp++] = val[d][i];
        }
    }

    build(l, mid, d+1);
    build(mid+1, r, d+1);
}

int query(int a, int b, int k, int l, int r, int d)
{
    if(a == b)  return val[d][a];

    int mid = (l + r) >> 1;
    int s, ss;

    if(a == l)
    {
        s = tlsum[d][b];
        ss = 0;
    }
    else
    {
        s = tlsum[d][b] - tlsum[d][a-1];
        ss = tlsum[d][a-1];
    }

    if(s >= k)
    {
        a = l + ss;
        b = l + s + ss - 1;
        return query(a, b, k, l, mid, d+1);
    }

    else
    {
        a = mid + 1 + a - l - ss;
        b = mid + 1 + b - l - tlsum[d][b];
        return query(a, b, k-s, mid+1, r, d+1);
    }
}

int main()
{
    int n, m, c, s, t, k;

    scanf("%d", &c);

    while(c--)
    {
        scanf("%d%d", &n, &m);

        for(int i=1; i<=n; ++i)
        {
            scanf("%d", &sorted[i]);
            val[0][i] = sorted[i];
        }

        sort(sorted+1, sorted+1+n);
        build(1, n, 0);

        while(m--)
        {
            scanf("%d%d%d", &s, &t, &k);

            printf("%d\n", query(s, t, k, 1, n, 0));
        }
    }

    return 0;
}