Find First and Last Position of Element in Sorted Array Problem


Description

LeetCode Problem 34.

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:

1
2
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]

Example 2:

1
2
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

Example 3:

1
2
Input: nums = [], target = 0
Output: [-1,-1]

Constraints:

  • 0 <= nums.length <= 10^5
  • -10^9 <= nums[i] <= 10^9
  • nums is a non-decreasing array.
  • -10^9 <= target <= 10^9


Sample C++ Code

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
vector<int> searchRange(vector<int>& nums, int target) {
    int idx1 = lower_bound(nums, target);
    int idx2 = lower_bound(nums, target+1)-1;
    if (idx1 < nums.size() && nums[idx1] == target)
        return {idx1, idx2};
    else
        return {-1, -1};
}

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




Related Posts

Super Egg Drop Problem

LeetCode 887. You are given k identical eggs and you...

Peak Index In A Mountain Array Problem

LeetCode 852. Let’s call an array arr a mountainif the...

Numbers At Most N Given Digit Set Problem

LeetCode 902. Given an array of digits which is sorted...

Nth Magical Number Problem

LeetCode 878. A positive integer is magical if it is...

Reach A Number Problem

LeetCode 754. You are standing at position 0 on an...