Search for a Range

二分

    vector<int> searchRange(int A[], int n, int target) {
        // Note: The Solution object is instantiated only once and is reused by each test case
        vector<int> res(2,-1);
        int firstpos = findFirstPos(A,0,n-1,target);
        if(firstpos!=-1){
            int lastpos = findLastPos(A,0,n-1,target);
            res[0] = firstpos;
            res[1] = lastpos;
        }
        return res;
        
    }
    
    int findFirstPos(int A[], int begin,int end, int target)
    {
        int mid;
        while(begin<end)
        {
            mid = begin + (end-begin)/2;
            if(A[mid]<target)
                begin = mid+1;
            else
                end = mid;
        }
        return (A[begin]==target?begin:-1);
    }
    
    int findLastPos(int A[],int begin,int end,int target)
    {
        int mid;
        while(begin<end)
        {
            mid = begin+(end-begin+1)/2;
            if(A[mid]>target)
                end = mid-1;
            else
                begin = mid;
        }
        return (A[begin]==target?begin:-1);
    }