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

用binary search

對兩邊做兩遍

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