leetcode个人题解——#34 Find First and Last Position of Element in Sorted Array

思路：先二分查找到一个和target相同的元素，然后再左边二分查找左边界，右边二分查找有边界。

class Solution {
public:
    int begin  = -, end = -;
    int ends;
    int lSearch(int left, int right, vector<int>& nums, int target)
    {
        if(left > right) return -;
        int mid = (left + right) / ;
        if(nums[mid] == target){
            if(mid ==  || (mid >  && nums[mid - ] < target)) return mid;
            else return lSearch(left,mid - ,nums,target);
        }else
            return lSearch(mid + ,right,nums,target);
        return -;
    }

    int rSearch(int left, int right, vector<int>& nums, int target)
    {
        if(left > right) return -;
        int mid = (left + right) / ;
        if(nums[mid] == target){
            if(mid == ends || (mid < ends && nums[mid + ] > target)) return mid;
            else return rSearch(mid + ,right,nums,target);
        }else
            return rSearch(left ,mid - ,nums,target);
        return -;
    }

    int midSearch(int left, int right, vector<int>& nums, int target)
    {
        if(left > right) return -;
        int mid = (left + right) / ;
        if(nums[mid] == target){
            return mid;
        }
        else if(nums[mid] < target) return midSearch(mid + ,right,nums,target);
        else if(nums[mid] > target) return midSearch(left, mid - ,nums,target);
        return -;
    }

    vector<int> searchRange(vector<int>& nums, int target) {
        ends = nums.size() - ;
        int mid = midSearch(,ends,nums,target);
        if(mid != -){
        begin = lSearch(,mid,nums,target);
        end = rSearch(mid,ends,nums,target);
        }
        vector<int> ans;
        ans.push_back(begin);
        ans.push_back(end);
        return ans;
    }
};