第二大的数

int find_second_biggest(vector<int> &v){
        int len = v.size();
        int max,second;
        if (len < 2){
                return -1; 
        }
        if (v[0]>v[1]){ 
                second = v[1];
                max = v[0];
        }
        else{
                second = v[0];
                max = v[1];
        }
        for (int i=2; i< len; i++){
                if(max < v[i]){
                        second = max;
                        max = v[i];
                }
                else if (second < v[i]){
                        second = v[i];
                }
        }
        return second;
}