09 Sept 2026•Easy•Go / Python / TypeScript

Height Checker

Count positions whose heights differ from the nondecreasing expected order.

Sort a copy of the heights and count index-wise differences from the original arrangement.

Complexity

O(n log n) time and O(n) space.

Solution files

Go•height-checker/solution.go

package main

import "sort"

func heightChecker(heights []int) int {
	expected := append([]int(nil), heights...)
	sort.Ints(expected)
	mismatches := 0
	for index, height := range heights {
		if height != expected[index] {
			mismatches++
		}
	}
	return mismatches
}

Python•height-checker/solution.py

class Solution:
    def heightChecker(self, heights: list[int]) -> int:
        return sum(actual != expected for actual, expected in zip(heights, sorted(heights)))

TypeScript•height-checker/solution.ts

function heightChecker(heights: number[]): number {
  const expected = [...heights].sort((left, right) => left - right);
  return heights.reduce((count, height, index) => count + Number(height !== expected[index]), 0);
}