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leetcode 二分法通用解法

class Soultion
{
public:
    int binarySearch(vector<int>&nums, int target)
    {
        if (nums.size() == 0)
        {
            return -1;
        }
        int start = 0;
        int end = nums.size() - 1;
        int mid;
        while (start + 1 < end)/*避免相交或者相邻*/
        {
            mid = start + (end - start) / 2;
            //start+end/2这种方法MAXINT可能会移除
            if (nums[mid] == target) {
                end = mid;
            }
            else if (nums[mid] < target)
            {
                start = mid;
            }
            else if (nums[mid] > target)
            {
                end = mid;
            }
        }
        //判断取得是第一个还是第二个
        if (nums[start] == mid)
        {
            return start;
        }
        if (nums[end] == mid)
        {
            return end;
        }
        return -1;
    }
};