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3616. Number of Student Replacements 🔒

Description

You are given an integer array ranks where ranks[i] represents the rank of the ith student arriving in order. A lower number indicates a better rank.

Initially, the first student is selected by default.

A replacement occurs when a student with a strictly better rank arrives and replaces the current selection.

Return the total number of replacements made.

 

Example 1:

Input: ranks = [4,1,2]

Output: 1

Explanation:

  • The first student with ranks[0] = 4 is initially selected.
  • The second student with ranks[1] = 1 is better than the current selection, so a replacement occurs.
  • The third student has a worse rank, so no replacement occurs.
  • Thus, the number of replacements is 1.

Example 2:

Input: ranks = [2,2,3]

Output: 0

Explanation:

  • The first student with ranks[0] = 2 is initially selected.
  • Neither of ranks[1] = 2 or ranks[2] = 3 is better than the current selection.
  • Thus, the number of replacements is 0.

 

Constraints:

  • 1 <= ranks.length <= 105​​​​​​​
  • 1 <= ranks[i] <= 105

Solutions

Solution 1: Simulation

We use a variable $\text{cur}$ to record the rank of the currently selected student. We iterate through the array $\text{ranks}$, and if we encounter a student with a better rank (i.e., $\text{ranks}[i] < \text{cur}$), we update $\text{cur}$ and increment the answer by one.

After the iteration, we return the answer.

The time complexity is $O(n)$, where $n$ is the number of students. The space complexity is $O(1)$.

  • class Solution {
    public int totalReplacements(int[] ranks) {
        int ans = 0;
        int cur = ranks[0];
        for (int x : ranks) {
            if (x < cur) {
                cur = x;
                ++ans;
            }
        }
        return ans;
    }
}

  • class Solution {
public:
    int totalReplacements(vector<int>& ranks) {
        int ans = 0;
        int cur = ranks[0];
        for (int x : ranks) {
            if (x < cur) {
                cur = x;
                ++ans;
            }
        }
        return ans;
    }
};

  • class Solution:
    def totalReplacements(self, ranks: List[int]) -> int:
        ans, cur = 0, ranks[0]
        for x in ranks:
            if x < cur:
                cur = x
                ans += 1
        return ans


  • func totalReplacements(ranks []int) (ans int) {
	cur := ranks[0]
	for _, x := range ranks {
		if x < cur {
			cur = x
			ans++
		}
	}
	return
}

  • function totalReplacements(ranks: number[]): number {
    let [ans, cur] = [0, ranks[0]];
    for (const x of ranks) {
        if (x < cur) {
            cur = x;
            ans++;
        }
    }
    return ans;
}

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