Height Checker

Height Checker

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

Constraints:

• 1 <= heights.length <= 100

• 1 <= heights[i] <= 100

Solutions

🧠 Cpp

#define all(x) (x).begin(), (x).end()
class Solution
{
public:
    int heightChecker(vector<int>& heights)
    {
        //O(N logN) solution (sorting)
        vector<int> sorted_h = heights;
        std::sort(all(sorted_h));

        unsigned counter = 0;
        for(int i = 0; i < heights.size(); ++i)
            if(heights[i] != sorted_h[i])
                ++counter;    

        return counter;
    }
};