例题详解Java dfs与记忆化搜索和分治递归算法的使用

/**
 * 深度优先搜索
 * 
 * @param node
 * @param set
 */
public void DFS(Node node, Set<Node> set) {
    if (node == null) {
        //当没有节点时，退出此次方法
        return;
    }
    if (!set.contains(node)) {
        //没有搜到过就保存，并且继续向下推进
        set.add(node);
        System.out.print(node.value + " ");
        for (Node node1 : node.nexts) {
            DFS(node1, set);
        }
    }
}

public static void dfs(Node treeNode) {
        if (treeNode == null) {
            return;
        }
        System.out.print(treeNode.value + " ");
        // 遍历左节点
        dfs(treeNode.left);
        // 遍历右节点
        dfs(treeNode.right);
    }

public static int f(int n){
    if(n<=1)return 1;
    return f(n-1)+f(n-2);
}

    static int[] dp = new int[1000] ;
    public static int f1(int n){
        if(n<=1) return dp[n] = 1;
        if(dp[n]!=0)return dp[n];
        return dp[n]=f1(n-1)+f1(n-2);
    }

import java.util.*;
import java.io.*;
public class Main{
    static class Edge{
        int to;
        int weight;
        //保存子节点，与线权（传播时间）。
        Edge(int to,int weight){
            this.to = to;
            this.weight = weight;
        }
    }
    static ArrayList<Edge>[] g;
    static int maxtime;
    static int weight[];
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine()); //n为总人数
        weight = new int[n+1];
        g = new ArrayList[n+1];
        // 每个桶中保存一个ArrayList（可达）
        //这里的i代表了第几个数（从1开始）
        for(int i = 1;i<=n;i++){
            g[i] = new ArrayList();
        }
        //保存所有点权（理解时间）纪录了从2到n的点权，与数字的位子相对应。
        String[] s = br.readLine().split(" ");
        for(int i = 0;i<n-1;i++){
            weight[i+2] = Integer.parseInt(s[i]);
        }
        for(int i = 0;i<n-1;i++){
            String[] s1 = br.readLine().split(" ");
            int x = Integer.parseInt(s1[0]);
            int y = Integer.parseInt(s1[1]);
            int z = Integer.parseInt(s1[2]);
            g[x].add(new Edge(y,z));
        }
        dfs(1,0);
        System.out.println(maxtime);
    }
    static void dfs(int i ,int time){
        if(maxtime<time+weight[i])maxtime = time+weight[i];
        for(int k = 0;k<g[i].size();k++){
            dfs(g[i].get(k).to,time+g[i].get(k).weight);
        }
    }
}

import java.util.*;
import java.io.*;
 
public class Main {
    static ArrayList<Integer>[] g;
    static String[] strings;
    static int[] visited;
 
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] firstLine = br.readLine().split(" ");
        int n = Integer.parseInt(firstLine[0]);
        int m = Integer.parseInt(firstLine[1]);
        g = new ArrayList[n+1];
        visited = new int[n+1];
        for (int i=1;i<n+1;i++) {
            g[i] = new ArrayList<Integer>();
        }
        //一个字符一个字符的读取
        strings = br.readLine().split("");
        for (int i=0;i<m;i++) {
            //描绘双向图
            String[] temp = br.readLine().split(" ");
            int x = Integer.parseInt(temp[0]);
            int y = Integer.parseInt(temp[1]);
            g[x].add(y);
            g[y].add(x);
        }
        int cnt = 0;
        StringBuilder sb = new StringBuilder();
        for (int i=1;i<n+1;i++) {
            if (visited[i] ==0 && strings[i-1].equals("R")) {
                cnt++;
                sb.append(i + " ");
                //从糖葫芦小的开始纪录，然后延深。
                dfs(i);
            }
        }
        System.out.println(cnt);
        System.out.println(sb);
    }
 
    static void dfs(int x) {
        if (visited[x] ==0 && strings[x-1].equals("R")) {
            //点亮它
            visited[x] = 1;
            for (int i=0;i<g[x].size();i++) {
                dfs(g[x].get(i));
            }
        }
    }
}

import java.util.*;
import java.io.*;
 
public class Main{
    static boolean[] check = new boolean[2000];
    static int[] ai;
    static int n;
    static int min = Integer.MAX_VALUE;
    //判断是否为素数
    static boolean isPrime(int x){
        if(x<2) return false;
        //这是根据开根号的演化版本，提高了效率。
        for(int i=2;i*i<=x;i++){
            if(x%i==0)return false;
        }
        return true;
    }
    static void dfs(int index,int sum){
        if(index==n){
            min=Math.min(min,sum);
            return;
        }
        //查找这个数没有被占用的素因子。
        for(int i=2;i<=ai[index];i++){
            if(ai[index]%i==0&&check[i]==false&&isPrime(i)){
                check[i]=true;
                dfs(index+1,sum+i);
                //回溯的方法。
                check[i]=false;
            }
        }
    }
    public static void main(String[] args)throws IOException{ 
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.parseInt(br.readLine());
        String[] a = br.readLine().split(" ");
        //负责保存所有输入的数
        ai = new int[n];
        for(int i=0;i<n;i++){
            ai[i]=Integer.parseInt(a[i]);
        }
        dfs(0,0);
        System.out.println(min==Integer.MAX_VALUE ? -1:min);
        br.close();
    }
}

import java.util.*;
import java.io.*;
public class Main{
    static HashMap<Long,Long> map = new HashMap<>();
    public static void main (String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int num = Integer.parseInt(br.readLine());
        for(int i = 0; i<num; i++){
            System.out.println(recurse(Long.parseLong(br.readLine())));
        }
    }
    static long recurse(long num){
        if(num <= 1) return 0;
        //用于保存
        if(map.containsKey(num)) return map.get(num);
        long pay = recurse(num/2) + recurse(num-num/2) +num%2;
        map.put(num,pay);
        return pay;
    }
}