实现下面C++函数：

下面是一种O（n）的实现方法。

#include <iostream>
#include <string>
#include <map>
#include <vector>
using namespace std;
int getMaxLen(string& src){
	map< vector<int> ,vector<int> > j;
	//vector<int> k,m;
	int a_index=0;
	int b_index=0;
	int c_index=0;
	int ba_minus;
	int ca_minus;
	vector<int> vo,vo_value;
	vo.push_back(0);
	vo.push_back(0);
	vo_value.push_back(-1);
	j.insert(make_pair(vo,vo_value));
	for(int i=0;i<src.length();i++){
		if (src[i]=='a') a_index++;
		if (src[i]=='b') b_index++;
		if (src[i]=='c') c_index++;
		ba_minus=b_index-a_index;
		ca_minus=c_index-a_index;
		vector<int> k;
		k.clear();
		k.push_back(ba_minus);
		k.push_back(ca_minus);
		map< vector<int> ,vector<int> >::iterator find_flag=j.find(k);
		if(find_flag!=j.end()){
			find_flag->second.push_back(i);
		}
		else{
			vector<int> m;
			m.push_back(i);
			j.insert(make_pair(k,m));
		}
	}
	map< vector<int>, vector<int> >::iterator bianli=j.begin();
	int max=0;
	while(bianli!=j.end()){
		if(bianli->second.size()>=2){
			int minus=bianli->second[bianli->second.size()-1]-bianli->second[0];
			cout<<bianli->second[bianli->second.size()-1]<<endl;
			cout<<bianli->second[0]<<endl;
			if(minus>max) max=minus;
		}
		bianli++;
	}
	return max;	
}
int main(){
	string test="abcabcabcabc";
	cout<<getMaxLen(test)<<endl;
	return 0;

}

求字符串中满足所有字符个数相等的最长子串长度