二分查找法

前言
在笔试的时候，二分查找法容易写错一些细节导致最后的结果是错的；

// 该二分查找的目的是在一个有序序列中找到第一个大于等于target的下标
int bin_find(vector nums, int target)
{
    int start = 0, end = nums.size() - 1;
    bool is_find = false;
    if (target <= nums[start]) return start;
    if (target > nums[end]) return -1;
    while (start <= end) {
        int mid = (start + end) / 2;
        if (mid > 0 && nums[mid] >= target && nums[mid - 1] < target) {
            return mid;
        }
        if (nums[mid] > target)
            end = mid - 1;
        else
            start = mid + 1;
    }
    return -1;
}

// 二分查找法，判断一个数是否存在于一个有序序列中
int binary_find_exist(vector nums, int target)
{
    int start = 0, end = nums.size() - 1;
    while (start <= end) {
        int mid = (start + end) / 2;
        if (nums[mid] == target)
            return mid;
        else if (nums[mid] > target)
            end = mid - 1;
        else
            start = mid + 1;
    }
    return -1;
}

int main() {
    vector temp({1,2,4,6,7,9,11});
    int index = bin_find(temp, 7);
    if (index == -1)
        cout << "can not find!!!" << endl;
    else
        cout << "index = " << index << "   nums[index] = "<< temp[index] << endl;
    return 0;
}