2023-10-09 Daily Challenge

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In: DailyChallenge

Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 9

Description

Find First and Last Position of Element in Sorted Array

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

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

You must write an algorithm with O(log n) runtime complexity.

 

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]

Example 3:

Input: nums = [], target = 0
Output: [-1,-1]

 

Constraints:

  • 0 <= nums.length <= 105
  • -109 <= nums[i] <= 109
  • nums is a non-decreasing array.
  • -109 <= target <= 109

Solution

class Solution {
public:
  vector<int> searchRange(vector<int>& nums, int target) {
    int len = nums.size();
    if(!len) return{-1, -1};
    int begin = 0;
    int end = len - 1;
    while(begin < end) {
      int mid = (begin + end) >> 1;
      if(nums[mid] < target) {
        begin = mid + 1;
      } else {
        end = mid;
      }
    }
    if(nums[begin] != target) return {-1, -1};
    int left = begin;
    begin = 0;
    end = len - 1;
    while(begin < end) {
      int mid = (begin + end + 1) >> 1;
      if(nums[mid] > target) {
        end = mid - 1;
      } else {
        begin = mid;
      }
    }
    return {left, begin};
  }
};

// Accepted
// 88/88 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 25.3 % of cpp submissions (14 MB)
Algorithm