Java每日一练(20230403) 字母异位词分组、删除链表的倒数第 N 个结点、合并区间

import java.util.*;
public class groupAnagrams {
    public static List<List<String>> groupAnagrams(String[] strs) {
        HashMap<String, ArrayList<String>> map = new HashMap<>();
        for (String str : strs) {
            char[] cs = str.toCharArray();
            Arrays.sort(cs);
            String key = String.valueOf(cs);
            if (!map.containsKey(key)) {
                map.put(key, new ArrayList<>());
            }
            map.get(key).add(str);
        }
        return new ArrayList<>(map.values());
    }
    public static List<List<String>> groupAnagrams2(String[] strs) {
        if (strs.length <= 0) {
            return new ArrayList<>();
        }
        HashMap<String, ArrayList<String>> map = new HashMap<>();
        for (String str : strs) {
            char[] cs = str.toCharArray();
            int[] count = new int[26];
            for (char c : cs) {
                ++count[c - 'a'];
            }
            StringBuilder s = new StringBuilder("");
            for (int num : count) {
                s.append(num);
            }
            String key = String.valueOf(s);
            if (!map.containsKey(key)) {
                map.put(key, new ArrayList<>());
            }
            map.get(key).add(str);
        }
        return new ArrayList<>(map.values());
    }
    public static void main(String[] args) {
        String[] words = {"eat", "tea", "tan", "ate", "nat", "bat"};
        for (List<String> word : groupAnagrams(words)) {
            System.out.print(word);
            System.out.print("");
        }
        System.out.println();
        for (List<String> word : groupAnagrams2(words)) {
            System.out.print(word);
            System.out.print("");
        }
        System.out.println();
    }
}

import java.util.*;
public class removeNthFromEnd {
    public static class ListNode {
        int val;
        ListNode next;
        ListNode() {
        }
        ListNode(int val) {
            this.val = val;
        }
        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }
    public static class Solution {
        public ListNode removeNthFromEnd(ListNode head, int n) {
            ListNode v = new ListNode(0, head);
            ListNode handle = v;
            List<ListNode> index = new ArrayList<>();
            while (v != null) {
                index.add(v);
                v = v.next;
            }
            int pre = index.size() - n - 1;
            int next = index.size() - n + 1;
            index.get(pre).next = next >= 0 && next < index.size() ? index.get(next) : null;
            return handle.next;
        }
    }
    public static ListNode[] arraysToLists(int[][] nums) {
        ListNode[] lists = new ListNode[nums.length];
        for (int i = 0; i < nums.length; i++) {
            int[] arr = nums[i];
            ListNode head = new ListNode(0);
            ListNode cur = head;
            for (int num : arr) {
                cur.next = new ListNode(num);
                cur = cur.next;
            }
            lists[i] = head.next;
        }
        return lists;
    }
    public static void traverseList(ListNode head) {
        ListNode cur = head;
        int count = 0;
        while (cur != null) {
            count++;
            cur = cur.next;
        }
        System.out.print("[");
        for (cur = head; cur != null;) {
            System.out.print(cur.val);
            count--;
            if (count>0) {
                System.out.print(",");
            }
            cur = cur.next;
        }
        System.out.println("]");
    }
    public static void main(String[] args) {
        Solution s = new Solution();
        int[][] lists = {{1,2,3,4,5},{1},{1,2}};
        int[] n = {2,1,1}; //对应链表的倒数n值
        ListNode[] heads = arraysToLists(lists);
        List<ListNode> res = new ArrayList<>();
        for (int i = 0; i < n.length; i++) {
            res.add(s.removeNthFromEnd(heads[i], n[i]));
            traverseList(res.get(i));
        }
    }
}

import java.util.*;
public class mergeIntervals {
    public static class Solution {
        public int[][] merge(int[][] intervals) {
            List<int[]> res = new ArrayList<>();
            if (intervals == null) {
                return res.toArray(new int[0][]);
            }
            Arrays.sort(intervals, (a, b) -> a[0] - b[0]);
            int i = 0;
            int left = 0;
            int right = 0;
            while (i < intervals.length) {
                left = intervals[i][0];
                right = intervals[i][1];
                while (i < intervals.length - 1 && right >= intervals[i + 1][0]) {
                    i++;
                    right = Math.max(right, intervals[i][1]);
                }
                res.add(new int[] { left, right });
                i++;
            }
            return res.toArray(new int[0][]);
        }
    }
    public static void PrintArrays(int[][] arr) {
        System.out.print("[");
        for (int i = 0; i < arr.length; i++) {
            System.out.print("[");
            for (int j = 0; j < arr[i].length; j++) {
                System.out.print(arr[i][j]);
                if (j < arr[i].length - 1) {
                    System.out.print(",");
                }
            }
            System.out.print("]");
            if (i < arr.length - 1) {
                System.out.print(",");
            }
        }
        System.out.println("]");
    }
    public static void main(String[] args) {
        Solution s = new Solution(); 
        int[][] intervals = {{1,3},{2,6},{8,10},{15,18}};
        PrintArrays(s.merge(intervals));
        int[][] intervals2 = {{1,4},{4,5}};
        PrintArrays(s.merge(intervals2));
    }
}