Algorithm: Leetcode Contest 406

3216. Lexicographically Smallest String After a Swap

Solution

class Solution {
    public String getSmallestString(String s) {
        char[] chars = s.toCharArray();
        
        for(int i = 0; i < chars.length - 1; i++) {
            if((chars[i] - '0') % 2 != (chars[i + 1] - '0') % 2) {
                continue;
            } else {
                if (chars[i] <= chars[i + 1]) {
                    continue;
                }
                char temp = chars[i];
                chars[i] = chars[i + 1];
                chars[i + 1] = temp;
                break;
            }
        }
        
        return new String(chars);
    }
}

3217. Delete Nodes From Linked List Present in Array

Solution

class Solution {
    public ListNode modifiedList(int[] nums, ListNode head) {
        // build hashset 
        Set<Integer> set = new HashSet<>();
        for(int num: nums) {
            set.add(num);
        }

        return remove(head, set);
    }
    
    private ListNode remove(ListNode head, Set<Integer> set) {
        // remove head
        while(head != null && set.contains(head.val)) {
            head = head.next;
        }
        
        if(head == null) {
            return null;
        }
        
        // head is pointing to first non-exist node
        ListNode cur = head.next, prev = head;
        // remove normal node
        while(cur != null) {
            if (!set.contains(cur.val)) {
                prev = cur;
                cur = cur.next;
            } else {
                prev.next = cur.next;
                cur = cur.next;
            }
        }
        
        return head;
    }
}

Retro

1. the way of removing node need more careful consideration