poj2104 K大数 划分树

#include <iostream>
#include <algorithm>
using namespace std;
const int M = 100005;
int toLeft[20][M], tree[20][M], sorted[M];

void build(int level, int left, int right)
{
if (left == right) return;
int i, mid = (left + right) >>1;
int suppose = mid - left + 1;
for (i=left; i<=right; i++)
if (tree[level][i] < sorted[mid])
suppose--;
int lpos = left, rpos = mid+1;
for (i=left; i<=right; i++)
{
if (i == left)
toLeft[level][i] = 0;
else
toLeft[level][i] = toLeft[level][i-1];
if (tree[level][i] < sorted[mid])
{
toLeft[level][i]++;
tree[level+1][lpos++] = tree[level][i];
}
else if (tree[level][i] > sorted[mid])
{
tree[level+1][rpos++] = tree[level][i];
}
else
{
if (suppose != 0)
{
suppose--;
toLeft[level][i]++;
tree[level+1][lpos++] = tree[level][i];
}
else
tree[level+1][rpos++] = tree[level][i];
}
}
build(level+1, left, mid);
build(level+1, mid+1, right);
}

int query(int level, int left, int right, int qleft, int qright, int k)
{
if (qleft == qright)
return tree[level][qright];
int s, ss, mid = (left + right)>>1;
if (left == qleft)
{
s = 0;
ss = toLeft[level][qright];
}
else
{
s = toLeft[level][qleft-1];
ss = toLeft[level][qright] - s;
}
int newl, newr;
if (k <= ss)
{
newl = left + s;
newr = left + s + ss -1;
return query(level+1, left, mid, newl, newr, k);
}
else
{
newl = mid-left+1+qleft-s;
newr = mid-left+1+qright-s-ss;
return query(level+1, mid+1, right, newl, newr, k-ss);
}
}

int main()
{
int n, m;
int i;
while (scanf("%d%d", &n, &m) == 2)
{
for (i=1; i<=n; i++)
{
scanf("%d", &tree[0][i]);
sorted[i] = tree[0][i];
}
sort(sorted+1, sorted+n+1);
build(0,1,n);
int ql, qr, k;
for (i=0; i<m; i++)
{
scanf("%d%d%d", &ql, &qr, &k);
printf("%d\n", query(0, 1, n, ql, qr, k));
}
}
return 0;
}