Remove Nth Node From End of List

1package pkg5leetcode.blind75;2 3/*4 * Remove Nth Node From End of List | LC 195 * APPROACH: Two pointers n+1 apart; delete node after slow.6 * COMPLEXITY: Time O(n), Space O(1)7 */8public class blind75_LC19RemoveNthNodeFromEnd {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 removeNthFromEnd(ListNode head, int n) {18        ListNode dummy = new ListNode(0);19        dummy.next = head;20        ListNode fast = dummy, slow = dummy;21        for (int i = 0; i <= n; i++) fast = fast.next;22        while (fast != null) { fast = fast.next; slow = slow.next; }23        slow.next = slow.next.next;24        return dummy.next;25    }26 27    static ListNode of(int... vals) {28        ListNode dummy = new ListNode(0), cur = dummy;29        for (int v : vals) { cur.next = new ListNode(v); cur = cur.next; }30        return dummy.next;31    }32 33    static int[] toArray(ListNode head) {34        java.util.List<Integer> list = new java.util.ArrayList<>();35        while (head != null) { list.add(head.val); head = head.next; }36        return list.stream().mapToInt(Integer::intValue).toArray();37    }38 39    public static void main(String[] args) {40        check(java.util.Arrays.equals(toArray(removeNthFromEnd(of(1, 2, 3, 4, 5), 2)), new int[]{1, 2, 3, 5}), "case1");41        check(java.util.Arrays.equals(toArray(removeNthFromEnd(of(1), 1)), new int[]{}), "case2");42        System.out.println("all tests passed");43    }44 45    static void check(boolean cond, String name) {46        if (!cond) throw new AssertionError("FAILED: " + name);47        System.out.println("  PASS " + name);48    }49}