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  = -1,end = -1;
    int ends;
    int lSearch(int left,int right,vector<int>& nums,int target)
    {
        if(left > right) return -1;
        int mid = (left + right) / 2;
        if(nums[mid] == target){
            if(mid == 0 || (mid > 0 && nums[mid - 1] < target)) return mid;
            else return lSearch(left,mid - 1,nums,target);
        }else
            return lSearch(mid + 1,right,target);
        return -1;
    }
    
    int rSearch(int left,int target)
    {
        if(left > right) return -1;
        int mid = (left + right) / 2;
        if(nums[mid] == target){
            if(mid == ends || (mid < ends && nums[mid + 1] > target)) return mid;
            else return rSearch(mid + 1,target);
        }else
            return rSearch(left,target);
        return -1;
    }
    
    int midSearch(int left,int target)
    {
        if(left > right) return -1;
        int mid = (left + right) / 2;
        if(nums[mid] == target){
            return mid;
        } 
        else if(nums[mid] < target) return midSearch(mid + 1,target);
        else if(nums[mid] > target) return midSearch(left,target);
        return -1;
    }
    
    vector<int> searchRange(vector<int>& nums,int target) {
        ends = nums.size() - 1;
        int mid = midSearch(0,ends,target);
        if(mid != -1){
        begin = lSearch(0,mid,target);
        end = rSearch(mid,target);
        }
        vector<int> ans;
        ans.push_back(begin);
        ans.push_back(end);
        return ans;
    }
};