统计各个字符串出现次数进行判断

#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
using namespace std;
#define int long long
const int mod=1e+7;
signed main() {
    iostream::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    string s;cin>>s;
    vector<int> a(128);
    for(int i=0;i<s.length();i++){
        a[s[i]]++;
    }
    int ans=0,num=0;
    for(int i=0;i<128;i++){
        ans+=a[i]/2*2;
        if(a[i]%2==1)num++;
    }
    if(num>0){
        ans++;
    }
    cout<<ans<<endl;
    return 0;
 }