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

Find Peak Element Problem

LeetCode 162. A peak element is an element that is...

Find Minimum In Rotated Sorted Array Problem

LeetCode 153. Suppose an array of length n sorted in...

Find Minimum In Rotated Sorted Array II Problem

LeetCode 154. Suppose an array of length n sorted in...

Search in Rotated Sorted Array II Problem

LeetCode 81. There is an integer array nums sorted in...

Search A 2D Matrix Problem

LeetCode 74. Write an efficient algorithm that searches for a...

Find First and Last Position of Element in Sorted Array Problem

LeetCode 34. Given the array nums after the possible rotation...