[LeetCode 75] Sliding Window

Sat, 14 Feb 2026 00:00:00 +0900

643. Maximum Average Subarray I

public double findMaxAverage(int[] nums, int k) {

 double maxAverage = 0;
 double currentSum = 0;

 for(int i = 0; i < k; i++) currentSum += (double)nums[i];
 maxAverage = currentSum / k;

 for(int i = 1; i + k - 1 < nums.length; i++){
 currentSum -= (double)nums[i - 1];
 currentSum += (double)nums[i + k - 1];
 maxAverage = Math.max(maxAverage, currentSum / k);
 }
 return maxAverage;
}

return할 때만 타입 캐스팅, 평균 연산
i + k - 1 대신 i를 윈도우 끝으로 사용해서 단순화

public double findMaxAverage(int[] nums, int k) {
 int currentSum = 0;
 for (int i = 0; i < k; i++) currentSum += nums[i];
 int maxSum = currentSum;

 for (int i = k; i < nums.length; i++) {
 currentSum += nums[i] - nums[i - k];
 maxSum = Math.max(maxSum, currentSum);
 }

 return (double) maxSum / k;
}

1456. Maximum Number of Vowels in a Substring of Given Length

public int maxVowels(String s, int k) {

 char[] vowels = new char[]{'a', 'e', 'i', 'o', 'u'};
 int[] isVowel = new int[s.length()];

 int vowelCount = 0;
 for(int i = 0; i < k; i++){
 for(char c : vowels){
 if(s.charAt(i) == c) {
 isVowel[i] = 1;
 vowelCount++;
 break;
 }
 }
 }

 int maxVowelCount = vowelCount;
 for(int i = k; i < s.length(); i++){
 for(char c : vowels){
 if(s.charAt(i) == c) {
 isVowel[i] = 1;
 break;
 }
 }

 vowelCount += isVowel[i] - isVowel[i - k];
 maxVowelCount = Math.max(maxVowelCount, vowelCount);
 }

 return maxVowelCount;

}

char array 대신에 문자열을 indexOf로 탐색하면 isVowel 배열 사용하지 않아도 됨
공간 복잡도 O(n) -> O(1)

public int maxVowels(String s, int k) {
 int vowelCount = 0;
 for (int i = 0; i < k; i++) {
 if ("aeiou".indexOf(s.charAt(i)) != -1) vowelCount++;
 }

 int maxVowelCount = vowelCount;
 for (int i = k; i < s.length(); i++) {
 if ("aeiou".indexOf(s.charAt(i)) != -1) vowelCount++;
 if ("aeiou".indexOf(s.charAt(i - k)) != -1) vowelCount--;
 maxVowelCount = Math.max(maxVowelCount, vowelCount);
 }

 return maxVowelCount;
}

Sliding Window on @yeniful blog

[LeetCode 75] Sliding Window

643. Maximum Average Subarray I

1456. Maximum Number of Vowels in a Substring of Given Length

1004. Max Consecutive Ones III

1493. Longest Subarray of 1’s After Deleting One Element