# 「POJ-2104」K-th Number-主席树

You are working for Macrohard company in data structures department. After failing your previous task about key insertion you were asked to write a new data structure that would be able to return quickly k-th order statistics in the array segment.
That is, given an array $a[1…n]$ of different integer numbers, your program must answer a series of questions $Q(i, j, k)$ in the form: “What would be the k-th number in $a[i…j]$ segment, if this segment was sorted?”
For example, consider the array $a = (1, 5, 2, 6, 3, 7, 4)$. Let the question be $Q(2, 5, 3)$. The segment $a[2…5]$ is $(5, 2, 6, 3)$. If we sort this segment, we get $(2, 3, 5, 6)$, the third number is $5$, and therefore the answer to the question is $5$.

poj2104