HDU - 5172 GTY's gay friends （线段树+前缀和）

GTY has nn gay friends. To manage them conveniently, every morning he ordered all his gay friends to stand in a line. Every gay friend has a characteristic value aiai , to express how manly or how girlish he is. You, as GTY's assistant, have to answer GTY's queries. In each of GTY's queries, GTY will give you a range [l,r][l,r] . Because of GTY's strange hobbies, he wants there is a permutation [1..r−l+1][1..r−l+1] in [l,r][l,r]. You need to let him know if there is such a permutation or not.

Input

Multi test cases (about 3) . The first line contains two integers n and m ( 1≤n,m≤10000001≤n,m≤1000000 ), indicating the number of GTY's gay friends and the number of GTY's queries. the second line contains n numbers seperated by spaces. The ithith number aiai ( 1≤ai≤n1≤ai≤n ) indicates GTY's ithith gay friend's characteristic value. The next m lines describe GTY's queries. In each line there are two numbers l and r seperated by spaces ( 1≤l≤r≤n1≤l≤r≤n ), indicating the query range.

Output

For each query, if there is a permutation [1..r−l+1][1..r−l+1] in [l,r][l,r], print 'YES', else print 'NO'.

Sample Input

8 5
2 1 3 4 5 2 3 1
1 3
1 1
2 2
4 8
1 5
3 2
1 1 1
1 1
1 2

Sample Output

YES
NO
YES
YES
YES
YES
NO

题意：

问区间[l,r]内的元素是否可以构成从1到r-l+1的一个排列。

思路：

如果可以构成，则[l,r]的区间和一定等于（r-l+1）*（r-l+2）/2

先判断区间和，符合条件的再判断区间内有无重复元素

预处理出每个数字上一次出现的位置，存入pre中，由于数据较大，所以建线段树来查找[l,r]中pre的最大值，若该值

具体实现见代码

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