34. Find First and Last Position of Element in Sorted Array | LeetCode

 34. Find First and Last Position of Element in Sorted Array | LeetCode

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

class Solution

{

public:

  vector<int> searchRange(vector<int> &A, int target)

  {

    int n = A.size();

    int i = 0, j = n - 1;

    vector<int> ret(2, -1);

    if (n == 0)

      return ret;

    while (i < j)

    {

      int mid = (i + j) / 2;

      if (A[mid] < target)

        i = mid + 1;

      else

        j = mid;

    }

    if (A[i] != target)

      return ret;

    else

      ret[0] = i;

    j = n - 1;

    while (i < j)

    {

      int mid = (i + j) / 2 + 1;

      if (A[mid] > target)

        j = mid - 1;

      else

        i = mid;

    }

    ret[1] = j;

    return ret;

  }

};