## The challenge

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:3Explanation: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

**Constraints:**

`1 <= heights.length <= 100`

`1 <= heights[i] <= 100`

## The solution

The easiest way to solve this is to sort a copy of the array, then compare which values are different.

```
class Solution {
// our method
public int heightChecker(int[] heights) {
// clone the input array
int[] heights2 = Arrays.copyOf(heights, heights.length);
// sort the new array to compare against
Arrays.sort(heights2);
// keep a count to return
int count = ;
// loop through the input array
for (int i=; i<heights.length; i++) {
// if the sorted value doesn't match
// then increment
if (heights[i]!=heights2[i]) count++;
}
// return our count
return count;
}
}
```

Code language: Java (java)