34.在排序数组中查找元素的第一个和最后一个位置.cpp

/*
 * @lc app=leetcode.cn id=34 lang=cpp
 *
 * [34] 在排序数组中查找元素的第一个和最后一个位置
 * 
 * 二分模版题
 */

// @lc code=start
class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        if (nums.empty()) return {-1, -1};

        int l = 0, r = nums.size() - 1;
        while (l < r) {
            int mid = r + l >> 1;
            if (nums[mid] >= target) r = mid;
            else l = mid + 1;
        }

        if (nums[r] != target) return {-1, -1};

        int L = r;
        l = 0, r = nums.size() - 1;
        while (l < r) {
            int mid = r + l + 1>> 1;
            if (nums[mid] <= target) l = mid;
            else r = mid - 1;
        }

        return {L, r};
    }
};
// @lc code=end