POJ2104K-th Number(主席树)

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
using namespace std;
const int N = 100005;
struct Node
{
int ls, rs, w;
Node(){ls = rs = w = 0;}
}segTree[N*20];
int a
, b
, p
, root
, sz;
bool cmp(int i, int j)
{
return a[i] < a[j];
}
void build(int &rt, int l, int r, int x)
{
segTree[++sz] = segTree[rt];
rt = sz;
segTree[rt].w++;
if(l == r)
return ;
int m = (l+r) >> 1;
if(x <= m)
build(segTree[rt].ls, l, m, x);
else
build(segTree[rt].rs, m+1, r, x);
}
int query(int i, int j, int l, int r, int k)
{
if(l == r)
return l;
int num = segTree[segTree[j].ls].w - segTree[segTree[i].ls].w;
int m = (l+r) >> 1;
if(num >= k)
return query(segTree[i].ls, segTree[j].ls, l, m, k);
else
return query(segTree[i].rs, segTree[j].rs, m+1, r, k-num);
}
int main()
{
int n, m;
while(scanf("%d%d", &n, &m) != EOF)
{
root[0] = 0;
for(int i = 1; i <= n; i++)
{
scanf("%d", &a[i]);
p[i] = i;
}
sort(p+1, p+n+1, cmp);
for(int i = 1; i <= n; i++)
b[p[i]] = i;
sz = 0;
for(int i = 1; i <= n; i++)
{
root[i] = root[i-1];
build(root[i], 1, n, b[i]);
}
for(int i = 0; i < m; i++)
{
int x, y, k;
scanf("%d%d%d", &x, &y, &k);
int t = query(root[x-1], root[y], 1, n, k);
printf("%d\n", a[p[t]]);
}
}
return 0;
}