Java实现滑动窗口算法的示例代码

import java.util.HashSet;

public class LongestSubstringWithoutRepeatingChars {
    public int lengthOfLongestSubstring(String s) {
        int left = 0, right = 0, maxLength = 0;
        HashSet<Character> window = new HashSet<>();

        while (right < s.length()) {
            char c = s.charAt(right);
            if (!window.contains(c)) {
                window.add(c);
                maxLength = Math.max(maxLength, right - left + 1);
                right++;
            } else {
                window.remove(s.charAt(left));
                left++;
            }
        }

        return maxLength;
    }

    public static void main(String[] args) {
        LongestSubstringWithoutRepeatingChars solution = new LongestSubstringWithoutRepeatingChars();
        System.out.println(solution.lengthOfLongestSubstring("abcabcbb")); // Output: 3
    }
}

import java.util.ArrayDeque;
import java.util.Deque;

public class SlidingWindowMaximum {
    public int[] maxSlidingWindow(int[] nums, int k) {
        if (nums == null || nums.length == 0) return new int[0];
        int n = nums.length;
        int[] result = new int[n - k + 1];
        Deque<Integer> deque = new ArrayDeque<>();

        for (int i = 0; i < nums.length; i++) {
            // 移除窗口左侧已过期的元素
            if (!deque.isEmpty() && deque.peekFirst() < i - k + 1) {
                deque.pollFirst();
            }

            // 移除所有比当前元素小的元素，因为它们不会成为最大值
            while (!deque.isEmpty() && nums[deque.peekLast()] < nums[i]) {
                deque.pollLast();
            }

            deque.offerLast(i);

            // 当窗口达到大小 k 时，记录最大值
            if (i >= k - 1) {
                result[i - k + 1] = nums[deque.peekFirst()];
            }
        }

        return result;
    }

    public static void main(String[] args) {
        SlidingWindowMaximum solution = new SlidingWindowMaximum();
        int[] result = solution.maxSlidingWindow(new int[]{1,3,-1,-3,5,3,6,7}, 3);
        for (int r : result) {
            System.out.print(r + " ");
        }
        // Output: 3 3 5 5 6 7
    }
}