二分查找

给定一个排序的整数数组（升序）和一个要查找的整数target，用O(logn)的时间查找到target第一次出现的下标（从0开始），如果target不存在于数组中，返回-1。

class Solution {
public:
    /**
     * @param nums: The integer array.
     * @param target: Target to find.
     * @return: The first position of target. Position starts from 0.
     */
    int binarySearch(vector<int> &nums, int target) {
        // write your code here
        int low=0;
        int high=nums.size();
        int mid=(low+high)/2;
        int returnData = -1;
        while(low<=high)
        {
            if(nums[mid]<target)
            {
                low=mid+1;
                mid=(low+high)/2;
            }
                
            else if(nums[mid]>target)
            {
                high=mid-1;
                mid=(low+high)/2;
            }
            else
            {
                returnData = mid;
                high=mid-1;
                mid=(low+high)/2;
            }
        }
        if(low>high)
            return returnData;
    }
};

渣渣代码，随缘优化。