LeetCode C++ compiler issue. Return doesn't work

Question

I am now learning C++, and started with tasks in LeetCode. The task is binarySearch. Got an issue with return statement when target found. Here is my solution:

class Solution {
public:
    int search(vector<int>& nums, int target) {
        int mid = nums.size() / 2;
        while (mid < nums.size() && mid >= 0) {
            cout << mid << ' ' << nums[mid] << endl; //for debuging
            if (nums[mid] == target) {
                cout << "WTF";    //PRINTS
                return mid;       // Doesn't work!
            }
            else if (target > nums[mid]) {
                mid += mid / 2;
            } 
            else if (target < nums[mid]) {
                mid -= mid / 2;
            } 
        }
        return -1;
    }
};

The problem is with return mid;. The output on test case [-1,0,3,5,9,12], target=9 is

Time Limit Exceeded
2 5
3 9
WTF3 5
2 3
1 0
1 0
1 0
1 0...

So, if statement works, but function continues working after return command. I've tried to compile same code with g++ and everything works nice.

Answer 1

Your function implementation is wrong. For example when the vector nums contains only one element then the variable mid will not be changed

else if (target > nums[mid]) {
    mid += mid / 2;
} 
else if (target < nums[mid]) {
    mid -= mid / 2;
}

because the expression mid / 2 is equal to 0. As a result you will have an infinite loop.

The function can be implemented the following way

class Solution {
public:
    std::vector<int>::size_type search( const std::vector<int> &nums, int target ) 
    {
        std::vector<int>::size_type low = 0, high = nums.size();

        while ( low != high ) 
        {
            auto mid = low + ( high - low ) / 2;

            if ( target < nums[mid] ) 
            {
                high = mid;
            }
            else if ( nums[mid] < target ) 
            {
                low = mid + 1;
            } 
            else
            { 
                return mid;
            } 
        }

        return -1;
    }
};