Leetcode 34

34. Find First and Last Position of Element in Sorted Array
    Medium

1723

90

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Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.

Your algorithm’s runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

Example 1:

Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]
Example 2:

Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

solve the problem

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        vector<int> v ;
        if(nums.size()==0){
            v.push_back(-1);
            v.push_back(-1);
            return v;
        }
        
        int min = 0;
        int max = nums.size()-1;
        int mid;
        int find = -1;
        //find in or not in the nums
        for(;(min<=max);){
            mid = (min+max)/2;;
            if(nums[mid]==target){
                find = mid;
                break;
            }
            else if(nums[mid]>target){
                max = mid-1;
            }
            else{
                min = mid +1;
            }
        }
        if(find!=-1){
        
            v.push_back(find);
            v.push_back(find);
            //scan for front
            for(int i = find-1;i>=0;i--){
                if(nums[i]==target){
                    v[0]--;
                }
            }
            scan for end 
            for(int i = find+1;i<nums.size();i++){
                if(nums[i]==target){
                    v[1]++;
                }
            }
         
        }
        else{
            v.push_back(-1);
            v.push_back(-1);
        }
        return v;
        
    }
};