每日一题合法括号序列判断,求最小公倍数,两种排序方法,二叉树的最近公共祖先

合法括号序列判断

import java.util.*;

public class Parenthesis {
    public boolean chkParenthesis(String A, int n) {
        // write code here
        Stack<Character>stack=new Stack<>();
        char[]arr=A.toCharArray();
        for(char c:arr){
            if(c=='('){
                stack.push(')');
            } else if(stack.isEmpty()||stack.pop()!=c){
                return false;
            }
        }
        return stack.isEmpty();
    }
}

求最小公倍数

import java.util.*;
public class Main{
 public static long gcd (long a, long b) {
        if (b == 0){
            return a;
        }
        return gcd (b,a%b);
    }
    public static void main (String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextInt();
        long b = sc.nextInt();
        System.out.println(a*b/gcd(a,b));
    }

}

两种排序方法

import java.util.*;
public class Main{
    public static void main(String[]args){
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        String[]arr=new String[n];
        for(int i=0;i<n;i++){
            arr[i]=sc.nextLine();
        }
        if(isLength(arr)&&isDict(arr)){
            System.out.println("both");
        }
       else if(isLength(arr)&&!isDict(arr)){
            System.out.println("lengths");
        }
         else if(isDict(arr)&&!isLength(arr)){
            System.out.println("lexicographically");
        }
        else{
             System.out.println("none");
        }
    }
    public static boolean isLength(String[]arr){
        for(int i=0;i<arr.length-1;i++){
            if (arr[i].length() >=arr[i + 1].length()) {
                return false;
            }
        }
        return true;
    }
    public static boolean isDict(String []arr) {
       for(int i=0;i<arr.length-1;i++){
            if (arr[i].compareTo(arr[i +1]) >=0) {
           return false;
            }
        }
        return true;
    }
}

二叉树的最近公共祖先

public TreeNode nearestCommonAncestor (TreeNode root, TreeNode p, TreeNode q) {
        // write code here 
        if(root==null){
            return null;
        }
        if(root.val==p.val||root.val==q.val){
            return root;
        }
        TreeNode left=nearestCommonAncestor(root.left,p,q);
        TreeNode right=nearestCommonAncestor(root.right,p,q);
        if(left!=null&&right!=null){
            return root;
        }
        return left==null?right:left;
    }