20180201getnumberofk

class Solution {
public:
    int GetNumberOfK(vector<int> data ,int k) {
        int count=0;
        if(data.size()>0){
            int s=0,e=data.size()-1;
            int first=firstk(data,k,s,e);
            int last=lastk(data,k,s,e);
            if(first>-1&&last>-1)
                count=last-first+1;
        }
        return count;
    }
    int firstk(vector<int> data,int k,int s,int e){
        if(s>e)
            return -1;
        int m=(s+e)/2;
        if(data[m]==k){
            if(m>0&&data[m-1]!=k||m==0)
                return m;
            else
                e=m-1;
        }
        else if(data[m]>k)
            e=m-1;
        else
            s=m+1;
        return firstk(data,k,s,e);
    }
    int lastk(vector<int> data,int k,int s,int e){
        if(s>e)
            return -1;
        int m=(s+e)/2;
        if(data[m]==k){
            if(m<data.size()-1&&data[m+1]!=k||m==data.size()-1)
                return m;
            else
                s=m+1;
        }
        else if(data[m]<k)
            s=m+1;
        else
            e=m-1;
        return lastk(data,k,s,e);
    }
};