Middle of the Linked List

1package pkg5leetcode.interview150;2 3/*4 * Middle of the Linked List | LC 8765 * APPROACH: Slow/fast pointers; slow at middle when fast reaches end.6 * COMPLEXITY: Time O(n), Space O(1)7 */8public class interview150_LC876MiddleOfTheLinkedList {9    /** Same shape as pkg5leetcode/common/ListNode.java (nested for single-file runs). */10 11    static class ListNode {12        int val;13        ListNode next;14        ListNode(int val) { this.val = val; }15    }16 17    static ListNode middleNode(ListNode head) {18        ListNode slow = head, fast = head;19        while (fast != null && fast.next != null) {20            slow = slow.next;21            fast = fast.next.next;22        }23        return slow;24    }25 26    static ListNode of(int... vals) {27        ListNode dummy = new ListNode(0), cur = dummy;28        for (int v : vals) { cur.next = new ListNode(v); cur = cur.next; }29        return dummy.next;30    }31 32    public static void main(String[] args) {33        check(middleNode(of(1, 2, 3, 4, 5)).val == 3, "case1");34        check(middleNode(of(1, 2, 3, 4, 5, 6)).val == 4, "case2");35        System.out.println("all tests passed");36    }37 38    static void check(boolean cond, String name) {39        if (!cond) throw new AssertionError("FAILED: " + name);40        System.out.println("  PASS " + name);41    }42}