# [LeetCode]#1051. Height Checker

**Environment: Python 3.7**

**Key technique: zip, sorted, sum**

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.

**Analysis:**

- Sort heights as another list [1,1, 1, 2,3,4] .
- use zip ( sorted(heights), heights) to get pair as [ (1, 1), (1,1), (1,4),(2,2),(1,3),(3,4)].
- Summarize different pair and we get three.

**Solution:**

`class Solution:`

def heightChecker(self, heights):

return sum(h != sh for h, sh in zip(sorted(heights), heights))

**Submissions:**

**Reference:**