2022-7-7 Leetcode 34.在排序数组中查找元素的第一个和最后一个位置

1、左右区间要单独查找，时间复杂度为$O(logN)$
2、查找右边界的时候，左边向右收缩；查找左边界的时候，右边向左收缩。

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

    int getL(vector<int>& nums, int target){
    
        int l = 0, r = nums.size()-1;
        int leftborder = -1;
        while (l <= r){
    
            int mid = l + (r - l)/2;
            if (nums[mid] == target){
    
                r = mid - 1;
                leftborder = mid;
            }else if (nums[mid] > target){
    
                r = mid - 1;
            }else {
    
                l = mid + 1;
            }
        }
        return leftborder;
    }

    vector<int> searchRange(vector<int>& nums, int target) {
    
        int leftborder = getL(nums, target);
        int rightborder = getR(nums, target);
        return {
    leftborder, rightborder};
    }
};