The TopK problem of the number of occurrences of a string && base conversion && determines whether a list is palindromic

NC97 number of occurrences of the string TopK problem

Topic link

1

The string array is mapped, and then map.entrySet is placed into a list to sort the list.

2, code,

import java.util.*;


public class Solution {
    /**
     * return topK string
     * @paramStrings String One-dimensional array strings *@paramK int The integer the k *@returnString String two-dimensional array */
    public String[][] topKstrings (String[] strings, int k) {
        // write code here
        // write code here
        if (k == 0) {
            return new String[][]{};
        } else {
            String[][] res = new String[k][2];
            TreeMap<String, Integer> treeMap = new TreeMap<>();
            for (String str : strings) {
                if (treeMap.containsKey(str)) {
                    treeMap.put(str, treeMap.get(str) + 1);
                } else {
                    treeMap.put(str, 1);
                }
            }
            ArrayList<Map.Entry<String, Integer>> list = new ArrayList<>(treeMap.entrySet());
            Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
                @Override
                public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
                    if (o1.getValue() == o2.getValue()) {
                        if (o1.getKey().compareTo(o2.getKey()) < 0) {
                            return -1;
                        } else {
                            return 1; }}else {
                        returno2.getValue() - o1.getValue(); }}});for (int i = 0; i < k; i++) {
                res[i][0] = list.get(i).getKey();
                res[i][1] = String.valueOf(list.get(i).getValue());
            }
            returnres; }}}Copy the code

NC112 base conversion

Topic link

1

Common base processing, stack processing.

2, code,

import java.util.*;


public class Solution {
    /** * base conversion *@paramM int Specifies the integer *@paramN int The base to which the integer is converted *@returnString The character string */
    public String solve (int m, int n) {
        // write code here
        // write code here
        boolean isNeg = false;
        if (m < 0) {
            m *= -1;
            isNeg = true;
        }
        Stack<Integer> stack = new Stack<>();
        while(m ! =0) {
            stack.push(m % n);
            m = m / n;
        }
        StringBuilder stringBuilder = new StringBuilder();
        if (isNeg) {
            stringBuilder.append("-");
        }
        while(! stack.isEmpty()) {int val = stack.pop();
            if (val <= 9) {
                stringBuilder.append(val);
            } else {
                stringBuilder.append((char)(val - 10 + 65)); }}returnstringBuilder.toString(); }}Copy the code

NC96 determines whether a linked list is palindromic

Topic link

1

A clumsy approach is to group the list of numbers and then use a double pointer to determine whether the array is palindrome

2, code,

import java.util.*;

/* * public class ListNode { * int val; * ListNode next = null; *} * /

public class Solution {
    / * * * *@paramHead ListNode class The head *@returnBool Bool */
    private int getLen(ListNode node) {
        int ret = 0;
        ListNode temp = node;
        while(temp ! =null) {
            temp = temp.next;
            ret++;
        }
        return ret;
    }

    public boolean isPail(ListNode head) {
        // write code here
        int len = getLen(head);
        int[] arr = new int[len];
        int index = 0;
        ListNode temp = head;
        while(temp ! =null) {
            arr[index++] = temp.val;
            temp = temp.next;
        }
        int l = 0;
        int r = len - 1;
        while (l <= r) {
            if(arr[l] ! = arr[r]) {return false;
            }
            l++;
            r--;
        }
        return true; }}Copy the code