Height checker

Time: O(NlogN); Space: O(N); easy

Students are asked to stand in non-decreasing order of heights for an annual photo.

Return the minimum number of students that must move in order for all students to be standing in non-decreasing order of height.

Notice that when a group of students is selected they can reorder in any possible way between themselves and the non selected students remain on their seats.

Example 1:

Input: heights = [1,1,4,2,1,3]

Output: 3

Explanation:

  • Current array : [1,1,4,2,1,3]

  • Target array : [1,1,1,2,3,4]

  • On index 2 (0-based) we have 4 vs 1 so we have to move this student.

  • On index 4 (0-based) we have 1 vs 3 so we have to move this student.

  • On index 5 (0-based) we have 3 vs 4 so we have to move this student.

Example 2:

Input: heights = [5,1,2,3,4]

Output: 5

Example 3:

Input: heights = [1,2,3,4,5]

Output: 0

Notes:

  • 1 <= len(heights) <= 100

  • 1 <= heights[i] <= 100

[1]:

class Solution1(object):
    def heightChecker(self, heights):
        """
        :type heights: List[int]
        :rtype: int
        """
        return sum(i != j for i, j in zip(heights, sorted(heights)))

[2]:

s = Solution1()
heights = [1,1,4,2,1,3]
assert s.heightChecker(heights) == 3
heights = [5,1,2,3,4]
assert s.heightChecker(heights) == 5
heights = [1,2,3,4,5]
assert s.heightChecker(heights) == 0