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3616. Number of Student Replacements 🔒

题目描述

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

解法

方法一：模拟

我们用一个变量 \(\text{cur}\) 来记录当前选中的学生的排名。遍历数组 \(\text{ranks}\)，如果遇到一个排名更好的学生（即 \(\text{ranks}[i] < \text{cur}\)），则更新 \(\text{cur}\) 并将答案加一。

遍历结束后，返回答案即可。

时间复杂度 \(O(n)\)，其中 \(n\) 是学生的数量。空间复杂度 \(O(1)\)。

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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

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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;
    }
}

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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;
    }
};

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

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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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