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

這題其實就是把左右分開來找,

但會遇到一個麻煩

就是當你先找left, 可能會發生left太大根本不存在在這個list

所以你得卡一個left == num.size() 必須要直接結束

再來就是找right剛好相反過來, 可能這個值過小, right == -1時也可以直接return

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