二分查找中的边界问题：+1，-1，<,<=

class Solution {
public:
int GetNumberOfK(vector<int> data ,int k) {
int right=data.size()-1;
if (getLastk(data,k,0,right)==-1) return 0;
return  getLastk(data,k,0,right)-getFirstk(data,k,0,right)+1;
}

int getFirstk(vector<int>&data,int k,int left,int right){

while(left<=right){
int mid=(left+right)>>1;
if(data[mid]<k)
left=mid+1;//data[mid]!=k，所以k必然在[mid+1,right]之间，果断地+1，不要用left=mid;这里我们都用闭区间。
else if(data[mid]>k)
right=mid-1;
else if(mid-1>=0&&data[mid-1]==k)
right=mid-1;
else
return mid;
}
return -1;
}

/*
int getFirstk(vector<int>&data,int k,int left,int right){

if(left>right)  return -1;

int mid=(left+right)>>1;
if(data[mid]<k)
return getFirstk(data,k,mid+1,right);
else if(data[mid]>k)
return getFirstk(data,k,left,mid-1);
else if(mid-1>=left&&data[mid-1]==k)
return  getFirstk(data,k,left,mid-1);
else
return mid;

return -1;
}*/

int getLastk(vector<int>&data,int k,int left,int right){

while(left<=right){
int mid=(left+right)>>1;
if(data[mid]<k)
left=mid+1;
else if(data[mid]>k)
right=mid-1;
else if(mid+1<data.size()&&data[mid+1]==k)
left=mid+1;
else
return mid;
}
return -1;
}
};