leetcode+ 二分题目，返回下标

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//二分 
class Solution {
public:
    int searchInsert(vector<int>& nums, int target) {
        int l=0, r=nums.size()-1, pos = 0, mid =0;
        while (l<=r) {
            mid = (l+r)/2;
            if(nums[mid]==target) return mid;
            else if(target<nums[mid]){
                r = mid-1; pos = mid; //pos 设置
            }
            else if(target>nums[mid]){
                l = mid+1; pos=mid+1; //pos 设置
            }
        }
        return pos;
    }
};