Application scenarios of Java closures in data structures and algorithms

Closures are widely used in linked list inversion, tree structure traversal and dynamic programming in data structures and algorithms. By accessing and modifying outer scope variables, closures avoid the risk of recursive stack overflow when reversing linked lists; create custom iterators when traversing tree structures; in dynamic programming, closures are passed to recursion as memo parameters Function to store intermediate results.

Application scenarios of Java closures in data structures and algorithms

Closures are an important programming language feature that allow functions to access and modify Variables defined in the outer scope. This makes closures powerful in data structures and algorithms.

1. Linked List Reversal

One of the common solutions to reverse linked lists is to use closures. It can effectively reverse linked list elements while avoiding the risk of stack overflow caused by using recursion.

public class Node {
    int val;
    Node next;

    public Node(int val) {
        this.val = val;
    }
}

public static Node reverseList(Node head) {
    Node newHead = null;

    // 闭包函数，负责更新新链表指向
    Function<Node, Node> reverse = (prev) -> {
        if (head == null) {
            return prev;
        }

        Node next = head.next;
        head.next = prev;
        head = next;

        return reverse.apply(head);
    };

    return reverse.apply(newHead);
}

2. Tree structure traversal

Closures can be used to create custom iterators for traversing tree structures, such as pre-order traversal, in-order traversal and post-order traversal Order traversal.

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    public TreeNode(int val) {
        this.val = val;
    }
}

// 前序遍历
Function<TreeNode, List<Integer>> preOrder = (root) -> {
    if (root == null) {
        return Collections.emptyList();
    }

    List<Integer> result = new ArrayList<>();
    result.add(root.val);
    result.addAll(preOrder.apply(root.left));
    result.addAll(preOrder.apply(root.right));

    return result;
};

3. Dynamic Programming

The memo mode in the dynamic programming algorithm can effectively store intermediate results and avoid repeated calculations. Among them, closures can be used to pass memos as parameters to recursive functions.

public int fib(int n) {
    if (n <= 1) {
        return 1;
    }

    // 闭包函数，存储中间结果
    Function<Integer, Integer> memo = (x) -> {
        if (x <= 1) {
            return 1;
        } else if (memo.containsKey(x)) {
            return memo.get(x);
        } else {
            int result = fib(x - 1) + fib(x - 2);
            memo.put(x, result);
            return result;
        }
    };

    return memo.apply(n);
}

private Map<Integer, Integer> memo = new HashMap<>();

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