算法-查找鏈表中倒數第K個節點

鏈表數據結構

	public static class Node {
        private Node next;
        private int data;

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

算法實現

	public static Node findKthToTail(Node node, int k) {
        if (node == null || k <= 0) {
            return null;
        }

        Node p1 = node, p2 = node;
        // 先讓指針p1前進 k - 1個步, 指針p2不變
        for (int i = 0; i < k - 1; i++) {
            if (p1.next != null) {
                p1 = p1.next;
            } else {
                return null;
            }
        }
		// 此時p1處於第k步. 從第k步開始，兩個指針開始遍歷，當p1走到最後一個結點，p2正好是倒數第k個
        while (p1.next != null) {
            p1 = p1.next;
            p2 = p2.next;
        }
        return p2;
    }

打印節點信息

	public static void print(Node node) {
        while (node != null) {
            System.out.printf(node.data + "->");
            node = node.next;
        }
        System.out.println();
    }

驗證

	public static void main(String[] args) {
        Node node1 = new Node(1);
        Node node2 = new Node(2);
        Node node3 = new Node(3);
        Node node4 = new Node(4);
        Node node5 = new Node(5);
        Node node6 = new Node(6);
        Node node7 = new Node(7);
        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node5;
        node5.next = node6;
        node6.next = node7;

        print(node1);

        Node kthToTail = findKthToTail(node1, 3);
        System.out.println(kthToTail.data);
    }

1->2->3->4->5->6->7->
5