[leetcode] Majority Element

class Solution {
public:
int majorityElement(vector<int> &num) {
if(num.size()==0){
return -1;
}
int alternative=num[0];
int cnt=1;
for(int i=1;i<num.size();i++){
if(alternative==num[i]){
cnt++;
}else{
cnt--;
if(cnt==0){
alternative=num[i];
cnt=1;
}
}
}
//verify the result
cnt=0;
for(int j=0;j<num.size();j++){
if(alternative==num[j]){
cnt++;
}
}
if(cnt>num.size()/2){
return alternative;
}else{
return -1;
}
}
};