20. 有效的括号 - 力扣（LeetCode）
核心代码模式
class Solution {public boolean isValid(String s) {int len=s.length();Deque<Character> q=new ArrayDeque<>();for(char c:s.toCharArray()){//前置符号直接放if(c=='[')q.push(']');else if(c=='{')q.push('}');else if(c=='(')q.push(')');//为后置符号则直接取出来比较，不对直接返回falseelse if(q.isEmpty()||q.pop()!=c)return false;}//还有则falsereturn q.isEmpty();}
}
手写输入输出
import java.util.*;public class Javaacm
{
//输入格式
//()[]{}public static void main(String []args){Scanner scanner=new Scanner(System.in);String s=scanner.next();Deque<Character> st=new ArrayDeque<>();for(char c:s.toCharArray()){if(c=='[')st.push(']');else if(c=='{')st.push('}');else if(c=='(')st.push(')');else if(st.isEmpty()||st.pop()!=c){System.out.print(false);}}System.out.print(st.isEmpty());return ;}}
88. 合并两个有序数组 - 力扣（LeetCode）
核心代码模式
class Solution {public void merge(int[] nums1, int m, int[] nums2, int n) {m--;n--;//倒着比较插入for(int i=nums1.length-1;n>=0&&m>=0;i--){if(nums1[m]<=nums2[n])nums1[i]=nums2[n--];else nums1[i]=nums1[m--];}//如果1先比完则把2插进去while(n>=0)nums1[n]=nums2[n--];return ;}
}
手写输入输出
import java.util.*;public class Javaacm
{
//输入格式
// [1,2,3,0,0,0]
// 3
// [2,5,6]
// 3public static void main(String []args){Scanner scanner=new Scanner(System.in);String s=scanner.next();String[] str=s.substring(1,s.length()-1).split(",");int nums1[]=new int[str.length];int n1=scanner.nextInt();for(int i=0;i<n1;i++)nums1[i]=Integer.valueOf(str[i]);s=scanner.next();str=s.substring(1,s.length()-1).split(",");int nums2[]=new int[str.length];int n2=scanner.nextInt();for(int i=0;i<n2;i++)nums2[i]=Integer.valueOf(str[i]);n1--;n2--; for(int i=nums1.length-1;n1>=0&&n2>=0;i--){if(nums1[n1]<=nums2[n2])nums1[i]=nums2[n2--];else nums1[i]=nums1[n1--];}while(n2>=0)nums1[n2]=nums2[n2--];for(int i:nums1)System.out.print(i+" ");return ;}}
121. 买卖股票的最佳时机 - 力扣（LeetCode）
核心代码模式
class Solution {public int maxProfit(int[] prices) {int ans=0;int min=prices[0];for(int i:prices){ans=Math.max(ans,i-min);min=Math.min(min,i);}return ans;}
}
手写输入输出
import java.util.*;public class Javaacm
{
//输入格式
// [7,1,5,3,6,4]public static void main(String []args){Scanner scanner=new Scanner(System.in);String s=scanner.next();String[] str=s.substring(1,s.length()-1).split(",");int nums[]=new int[str.length];for(int i=0;i<nums.length;i++)nums[i]=Integer.valueOf(str[i]);int ans=0;int min=nums[0];for(int i:nums){ans=Math.max(ans,i-min);min=Math.min(min,i);}System.out.println(ans);return ;}}
103. 二叉树的锯齿形层序遍历 - 力扣（LeetCode）
核心代码模式
/*** Definition for a binary tree node.* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode() {}* TreeNode(int val) { this.val = val; }* TreeNode(int val, TreeNode left, TreeNode right) {* this.val = val;* this.left = left;* this.right = right;* }* }*/
class Solution {public List<List<Integer>> zigzagLevelOrder(TreeNode root) {List<List<Integer>> ans=new ArrayList<>();Queue<TreeNode> q=new ArrayDeque<>();if(root==null)return ans;q.offer(root);while(!q.isEmpty()){int n=q.size();List<Integer>layer =new ArrayList<>();for(int i=0;i<n;i++){TreeNode cur=q.poll();layer.add(cur.val);if(cur.left!=null)q.offer(cur.left);if(cur.right!=null)q.offer(cur.right);}ans.add(layer);}for(int i=1;i<ans.size();i+=2)Collections.reverse(ans.get(i));return ans;}
}
手写输入输出
import java.util.*;
class TreeNode
{TreeNode left,right;int val;TreeNode(int val){this.val=val;}TreeNode(String str){val=Integer.valueOf(str);}TreeNode(int val,TreeNode left,TreeNode right){this.val=val;this.left=left;this.right=right;}
}
public class Javaacm
{
//输入格式
// [3,9,20,null,null,15,7]public static void main(String []args){Scanner scanner=new Scanner(System.in);String s=scanner.next();if(s.equals("[]")){System.out.println("[]");return ;}String[] str=s.substring(1,s.length()-1).split(",");TreeNode root=buildtree(str,0);List<List<Integer>> ans=new ArrayList<>();Queue<TreeNode> q=new ArrayDeque<>();q.offer(root);while(!q.isEmpty()){int n=q.size();List<Integer> layer=new ArrayList<>();for(int i=0;i<n;i++){TreeNode cur=q.poll();layer.add(cur.val);if(cur.left!=null)q.offer(cur.left);if(cur.right!=null)q.offer(cur.right);}ans.add(layer);}for(int i=1;i<ans.size();i+=2)Collections.reverse(ans.get(i));System.out.println(ans);return ;}static TreeNode buildtree(String []str,int idx){if(idx>=str.length||str[idx].equals("null")){return null; }TreeNode root=new TreeNode(str[idx]);root.left=buildtree(str,2*idx+1);root.right=buildtree(str,2*idx+2);return root;}}
236. 二叉树的最近公共祖先 - 力扣（LeetCode）
核心代码模式
/*** Definition for a binary tree node.* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode(int x) { val = x; }* }*/
class Solution {public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {//只返回p,q,最近公共祖先三个节点，其余都为nullif(root==null||root==p||root==q)return root ;TreeNode l=lowestCommonAncestor(root.left,p,q);TreeNode r=lowestCommonAncestor(root.right,p,q);if(l!=null&&r!=null)return root;return l!=null?l:r;}
}
手写输入输出
import java.util.*;
class TreeNode
{TreeNode left,right;int val;TreeNode(int val){this.val=val;}TreeNode(String str){val=Integer.valueOf(str);}TreeNode(int val,TreeNode left,TreeNode right){this.val=val;this.left=left;this.right=right;}
}
public class Javaacm
{
//输入格式
//[3,5,1,6,2,0,8,null,null,7,4]
//5 1static int p,q;public static void main(String []args){Scanner scanner=new Scanner(System.in);String s=scanner.next();if(s.equals("[]")){System.out.println("[]");return ;}String[] str=s.substring(1,s.length()-1).split(",");TreeNode root=buildtree(str,0);p=scanner.nextInt();q=scanner.nextInt();System.out.println(findpq(root).val);return ;}static TreeNode findpq(TreeNode root){if(root==null||root.val==p||root.val==q)return root;TreeNode l=findpq(root.left);TreeNode r=findpq(root.right);if(l!=null&&r!=null)return root;return l!=null?l:r;}static TreeNode buildtree(String []str,int idx){if(idx>=str.length||str[idx].equals("null")){return null; }TreeNode root=new TreeNode(str[idx]);root.left=buildtree(str,2*idx+1);root.right=buildtree(str,2*idx+2);return root;}}
