A12369. Even Substrings
编程题
普及/提高-
知识点
题目描述
You are given a string $s=s_1s_2\dots s_n$ of length $n$ , which only contains digits $1$ , $2$ , ..., $9$ .
A substring $s[l \dots r]$ of $s$ is a string $s_l s_{l + 1} s_{l + 2} \ldots s_r$ . A substring $s[l \dots r]$ of $s$ is called even if the number represented by it is even.
Find the number of even substrings of $s$ . Note, that even if some substrings are equal as strings, but have different $l$ and $r$ , they are counted as different substrings.
A substring $s[l \dots r]$ of $s$ is a string $s_l s_{l + 1} s_{l + 2} \ldots s_r$ . A substring $s[l \dots r]$ of $s$ is called even if the number represented by it is even.
Find the number of even substrings of $s$ . Note, that even if some substrings are equal as strings, but have different $l$ and $r$ , they are counted as different substrings.
输入格式
The first line contains an integer $n$ ( $1 \le n \le 65000$ ) — the length of the string $s$ .
The second line contains a string $s$ of length $n$ . The string $s$ consists only of digits $1$ , $2$ , ..., $9$ .
The second line contains a string $s$ of length $n$ . The string $s$ consists only of digits $1$ , $2$ , ..., $9$ .
输出格式
Print the number of even substrings of $s$ .
输入输出样例
输入 #1
4 1234
输出 #1
6
输入 #2
4 2244
输出 #2
10
说明/提示
In the first example, the $[l, r]$ pairs corresponding to even substrings are:
- $s[1 \dots 2]$
- $s[2 \dots 2]$
- $s[1 \dots 4]$
- $s[2 \dots 4]$
- $s[3 \dots 4]$
- $s[4 \dots 4]$
In the second example, all $10$ substrings of $s$ are even substrings. Note, that while substrings $s[1 \dots 1]$ and $s[2 \dots 2]$ both define the substring "2", they are still counted as different substrings.
- $s[1 \dots 2]$
- $s[2 \dots 2]$
- $s[1 \dots 4]$
- $s[2 \dots 4]$
- $s[3 \dots 4]$
- $s[4 \dots 4]$
In the second example, all $10$ substrings of $s$ are even substrings. Note, that while substrings $s[1 \dots 1]$ and $s[2 \dots 2]$ both define the substring "2", they are still counted as different substrings.