1051. Height Checker
Description
A school is trying to take an annual photo of all the students. The students are asked to stand in a single file line in non-decreasing order by height. Let this ordering be represented by the integer array expected
where expected[i]
is the expected height of the ith
student in line.
You are given an integer array heights
representing the current order that the students are standing in. Each heights[i]
is the height of the ith
student in line (0-indexed).
Return the number of indices where heights[i] != expected[i]
.
Example 1:
Input: heights = [1,1,4,2,1,3] Output: 3 Explanation: heights: [1,1,4,2,1,3] expected: [1,1,1,2,3,4] Indices 2, 4, and 5 do not match.
Example 2:
Input: heights = [5,1,2,3,4] Output: 5 Explanation: heights: [5,1,2,3,4] expected: [1,2,3,4,5] All indices do not match.
Example 3:
Input: heights = [1,2,3,4,5] Output: 0 Explanation: heights: [1,2,3,4,5] expected: [1,2,3,4,5] All indices match.
Constraints:
1 <= heights.length <= 100
1 <= heights[i] <= 100
Solutions
Solution 1: Sorting
We can first sort the heights of the students, then compare the sorted heights with the original heights, and count the positions that are different.
The time complexity is $O(n \times \log n)$, and the space complexity is $O(n)$. Where $n$ is the number of students.
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Solution 2: Counting Sort
Since the height of the students in the problem does not exceed $100$, we can use counting sort. Here we use an array $cnt$ of length $101$ to count the number of times each height $h_i$ appears.
The time complexity is $O(n + M)$, and the space complexity is $O(M)$. Where $n$ is the number of students, and $M$ is the maximum height of the students. In this problem, $M = 101$.
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