算法与数据结构基础学习十一（暴力递归的尝试）

打印n层汉诺塔从最左边到最右边的的全部过程

public class Hanoi{
    public static void hanoi1(int n){
        leftToRight(n);
    }

    private static void leftToRight(int n){
        if (n == 1){
            System.out.println("Move 1 from left to right");
            return;
        }
        leftToMid(n-1);
        System.out.println("Move "+ n+" from left to right");
        midToRight(n-1);
    }

    private static void midToRight(int n){
        if (n ==1){
            System.out.println("Move 1 from mid to right");
            return;
        }
        midToLeft(n-1);
        System.out.println("Move "+n+" from mid to right");
        leftToRight(n-1);
    }

    private static void midToLeft(int n){
        if (n ==1){
            System.out.println("Move 1 from mid to left");
            return;
        }
        midToRight(n-1);
        System.out.println("Move "+n+" from mid to left");
        rightToLeft(n-1);
    }

    private static void rightToLeft(int n){
        if (n == 1){
            System.out.println("Move 1 from right to left");
            return;
        }
        rightToMid(n-1);
        System.out.println("Move "+n+" from right to left");
        midToLeft(n-1);
    }

    private static void rightToMid(int n){
        if (n == 1){
            System.out.println("Move 1 from right to mid");
            return;
        }
        rightToLeft(n-1);
        System.out.println("Move "+n+" from right to mid");
        leftToMid(n-1);
    }

    private static void leftToMid(int n){
        if (n ==1){
            System.out.println("Move 1 from left to mid");
            return;
        }
        leftToRight(n-1);
        System.out.println("Move "+n+" from left to mid");
        rightToMid(n-1);
    }

    public static void hanoi2(int n){
        if (n >0){
            func(n,"left","right","mid");
        }
    }

    private static void func(int n,String from,String to,String other){
        if (n ==1){
            System.out.println("Move 1 from "+from+" to "+to);
            return;
        }
        func(n-1,from,other,to);
        System.out.println("Move "+n+" from "+from+" to "+to);
        func(n-1,other,to,from);
    }

    public static void main(String[] args){
        int n =3;
        //hanoi1(n);
        hanoi2(n);
    }
}

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

public class PrintAllSubsquences{
    //打印一个字符串的全部子序列
    public static List subs(String s){
        char[] str = s.toCharArray();
        String path = "";
        List ans = new ArrayList<>();
        process1(str,0,ans,path);
        //process2(str,0,str.length,ans);
        return ans;
    }
    //打印一个字符串的全部子序列，要求不要出现重复字面值的子序列
    public static List subsNoRepeat(String s){
        char[] str = s.toCharArray();
        String path = " ";
        HashSet set = new HashSet<>();
        process2(str,0,set,path);
        List ans = new ArrayList<>();
        for (String cur :set){
            ans.add(cur);
        }
        return ans;
    }
    // str 固定参数
    // 来到了str[index]字符，index是位置
    // str[0..index-1]已经走过了！之前的决定，都在path上
    // 之前的决定已经不能改变了，就是path
    // str[index....]还能决定，之前已经确定，而后面还能自由选择的话，
    // 把所有生成的子序列，放入到ans里去
    private static void process1(char[] str,int index,List ans,String path){
        if (index == str.length){
            ans.add(path);
            return;
        }
        process1(str,index+1,ans,path);
        process1(str,index+1,ans,path+String.valueOf(str[index]));
    }
   private static void process2(char[] str,int index,HashSet set, String path){
        if (index == str.length){
            set.add(path);
            return;
        }
        String no = path;
        process2(str,index + 1,set,no);
        String yes = path+String.valueOf(str[index]);
        process2(str,index + 1,set,yes);
   }

    public static void main(String[] args){
        String test = "acccc";
        List ans1 = subs(test);
        List ans2 = subsNoRepeat(test);

        for (String str : ans1) {
            System.out.println(str);
        }
        System.out.println("=================");
        for (String str : ans2) {
            System.out.println(str);
        }
        System.out.println("=================");
    }
}

import java.util.ArrayList;
import java.util.List;

public class PrintAllPermutations{
    //打印一个字符串的全部排列
    public static List permutation1(String s){
        List ans = new ArrayList<>();
        if (s == null || s.length() == 0){
            return ans;
        }
        ArrayList rest = new ArrayList<>();
        char[] str = s.toCharArray();
        for (char ch : str){
            rest.add(ch);
        }
        String path = "";
        process1(rest,path,ans);
        return ans;
    }

    private static void process1(ArrayList rest,String path,List ans){
        if (rest.isEmpty()){
            ans.add(path);
        }else {
            int N = rest.size();
            for (int i = 0; i < N; i++) {
                char cur = rest.get(i);
                rest.remove(i);
                process1(rest,path+cur,ans);
                rest.add(i,cur);
            }
        }
    }


    public static List permutation2(String s){
        List ans = new ArrayList<>();
        if (s == null || s.length() == 0){
            return ans;
        }
        char[] str = s.toCharArray();
        process2(str,0,ans);
        return ans;
    }

    private static void process2(char[] str,int index,List ans){
        if (index == str.length){
            ans.add(String.valueOf(str));
        }else {
            for (int i = index; i < str.length; i++) {
                swap(str,index,i);
                process2(str,index+1,ans);
                swap(str,index,i);
            }
        }
    }

    private static void swap(char[] str,int index,int i){
        char tmp = str[index];
        str[index] = str[i];
        str[i] = tmp;
    }

    打印一个字符串的全部排列，要求不要出现重复的排列
    public static List permutation3(String s){
        List ans = new ArrayList<>();
        if (s == null || s.length() == 0){
            return ans;
        }
        char[] str = s.toCharArray();
        process3(str,0,ans);
        return ans;
    }

    private static void process3(char[] str,int index,List ans){
        if (index == str.length){
            ans.add(String.valueOf(str));
        }else {
            boolean[] visited = new boolean[256];
            for (int i = index; i 
                if (!visited[str[i]]){
                    visited[str[i]] = true;
                    swap(str,index,i);
                    process3(str,index+1,ans);
                    swap(str,index,i);
                }
            }
        }
    }
}

import java.util.Stack;

public class ReverseStackUsingRecursive{
    //给你一个栈，请你逆序这个栈，
    //不能申请额外的数据结构，
    // 只能使用递归函数。 如何实现?
    public static void reverse(Stack stack){
        if (stack.isEmpty()){
            return;
        }
        int i = f(stack); //取得当前栈的栈底
        reverse(stack);
        stack.push(i);
    }
    // 栈底元素移除掉
    // 上面的元素盖下来
    // 返回移除掉的栈底元素
    private static int f(Stack stack){
        int result = stack.pop();
        if (stack.isEmpty()){
            return result;
        }else {
            int last = f(stack);
            stack.push(result);
            return last;
        }
    }
    public static void main(String[] args) {
        Stack test = new Stack();
        test.push(1);
        test.push(2);
        test.push(3);
        test.push(4);
        test.push(5);
        reverse(test);
        while (!test.isEmpty()) {
            System.out.println(test.pop());
        }

    }
}

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