You are given a string??=?1?2…??s=s1s2…sn?of length??n, which only contains digits?11,?22, ...,?99.

A substring??[?…?]s[l…r]?of??s?is a string?????+1??+2…??slsl+1sl+2…sr. A substring??[?…?]s[l…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.

Input

The first line contains an integer??n?(1≤?≤650001≤n≤65000)?— the length of the string??s.

The second line contains a string??s?of length??n. The string??s?consists only of digits?11,?22, ...,?99.

Output

Print the number of even substrings of??s.

Examples input Copy 4 1234 output Copy 6 input Copy 4 2244 output Copy 10 Note

In the first example, the?[?,?][l,r]?pairs corresponding to even substrings are:

• ?[1…2]s[1…2]
• ?[2…2]s[2…2]
• ?[1…4]s[1…4]
• ?[2…4]s[2…4]
• ?[3…4]s[3…4]
• ?[4…4]s[4…4]

In the second example, all?1010?substrings of??s?are even substrings. Note, that while substrings??[1…1]s[1…1]?and??[2…2]s[2…2]?both define the substring "2", they are still counted as different substrings.

?

?題意：計數(shù)以偶數(shù)結(jié)尾的連續(xù)的子串的個數(shù)

?思路：遍歷一遍，如果當(dāng)前數(shù)字是偶數(shù)，則表示可以以它結(jié)尾，貢獻(xiàn)是它所在的位置大小，加到答案里就好。

?代碼：

#include <iostream> #include <cstdio> #include <cstdlib> #include <cmath> #include <cstring> #include <algorithm> #include <string> #include <vector> #include <queue> #include <stack> #include <set> #include <map> #define INF 0x3f3f3f3f #define ll long long #define ull unsigned long long #define lowbit(x) (x&(-x)) #define eps 0.00000001 #define PI acos(-1) #define ms(x,y) memset(x, y, sizeof(x)) using namespace std;const int maxn = 65005; char s[maxn];int main() {int n;cin >> n;scanf("%s", s+1);ll ans = 0;for(int i=1;i<=n;i++)if((s[i] - '0') % 2 == 0)ans += i;cout << ans << endl; }

　　

轉(zhuǎn)載于:https://www.cnblogs.com/HazelNut/p/10583477.html

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