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;
  }
};

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