B. Two-gram
Two-gram is an ordered pair (i.e. string of length two) of capital Latin letters. For example, “AZ”, “AA”, “ZA” — three distinct two-grams.
You are given a string s consisting of n capital Latin letters. Your task is to find any two-gram contained in the given string as a substring (i.e. two consecutive characters of the string) maximal number of times. For example, for string s = “BBAABBBA” the answer is two-gram “BB”, which contained in s three times. In other words, find any most frequent two-gram.
Note that occurrences of the two-gram can overlap with each other.
Input
The first line of the input contains integer number n (2≤n≤100) — the length of string s. The second line of the input contains the string s consisting of n capital Latin letters.
Output
Print the only line containing exactly two capital Latin letters — any two-gram contained in the given string s as a substring (i.e. two consecutive characters of the string) maximal number of times.
Examples
input
7
ABACABA
output
AB
input
5
ZZZAA
output
ZZ
Note
In the first example “BA” is also valid answer.
In the second example the only two-gram “ZZ” can be printed because it contained in the string “ZZZAA” two times.
这道题就是找给定字符串中的长度为2的连续子串出现的次数
str.substr(i,j) 从下标 i 开始，生成长度为 j 的子串
遍历map的时候需要
map<string,int> ma;
for(map<string,int>::iterator it = ma.begin(); it!=ma.end();++it)
{
cout<<it->first;
cout<<" "<<it->second<<endl;
}
#include<bits/stdc++.h>
using namespace std;
int main()
{
string str;
map<string,int> ma;
int len;
cin>>len>>str;
for(int i=0;i<len-1;++i)
ma[str.substr(i,2)]++;//str.substr(i,j) 从下标 i 开始，生成长度为 j 的子串
string ans;
int x = 0;
for(map<string,int>::iterator it = ma.begin(); it!=ma.end();++it)
{
if(it->second>=x)
{
x = it->second;
ans = it->first;
}
}
cout<<ans<<endl;
return 0;
}