A9001. Sereja and Subsequences
编程题
普及/提高-
知识点
题目描述
Sereja has a sequence that consists of $n$ positive integers, $a_{1},a_{2},...,a_{n}$ .
First Sereja took a piece of squared paper and wrote all distinct non-empty non-decreasing subsequences of sequence $a$ . Then for each sequence written on the squared paper, Sereja wrote on a piece of lines paper all sequences that do not exceed it.
A sequence of positive integers $x=x_{1},x_{2},...,x_{r}$ doesn't exceed a sequence of positive integers $y=y_{1},y_{2},...,y_{r}$ , if the following inequation holds: $x_{1}<=y_{1},x_{2}<=y_{2},...,x_{r}<=y_{r}$ .
Now Sereja wonders, how many sequences are written on the lines piece of paper. Help Sereja, find the required quantity modulo $1000000007$ $(10^{9}+7)$ .
First Sereja took a piece of squared paper and wrote all distinct non-empty non-decreasing subsequences of sequence $a$ . Then for each sequence written on the squared paper, Sereja wrote on a piece of lines paper all sequences that do not exceed it.
A sequence of positive integers $x=x_{1},x_{2},...,x_{r}$ doesn't exceed a sequence of positive integers $y=y_{1},y_{2},...,y_{r}$ , if the following inequation holds: $x_{1}<=y_{1},x_{2}<=y_{2},...,x_{r}<=y_{r}$ .
Now Sereja wonders, how many sequences are written on the lines piece of paper. Help Sereja, find the required quantity modulo $1000000007$ $(10^{9}+7)$ .
输入格式
The first line contains integer $n$ $(1<=n<=10^{5})$ . The second line contains $n$ integers $a_{1},a_{2},...,a_{n}$ $(1<=a_{i}<=10^{6})$ .
输出格式
In the single line print the answer to the problem modulo $1000000007$ $(10^{9}+7)$ .
输入输出样例
输入 #1
1 42
输出 #1
42
输入 #2
3 1 2 2
输出 #2
13
输入 #3
5 1 2 3 4 5
输出 #3
719