import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;public class AllStackPopOrder {public static LinkedList<String> allPermutation(String str){if(str == null || str.length() == 0)return null;//保存所有的全排列LinkedList<String> listStr = new LinkedList<String>();allPermutation(str.toCharArray(), listStr, 0);//print(listStr);//打印全排列return listStr;}private static void allPermutation(char[] c, LinkedList<String> listStr, int start){if(start == c.length-1)listStr.add(String.valueOf(c));else{for(int i = start; i <= c.length-1; i++){//只有当没有重叠的字符 才交换if(!isSwap(c, start, i)){swap(c, i, start);//相当于: 固定第 i 个字符allPermutation(c, listStr, start+1);//求出这种情形下的所有排列swap(c, start, i);//复位
                }}}}private static void swap(char[] c, int i, int j){char tmp;tmp = c[i];c[i] = c[j];c[j] = tmp;}private static void print(LinkedList<String> listStr){Collections.sort(listStr);//使字符串按照'字典顺序'输出for (String str : listStr) {System.out.println(str);}System.out.println("size:" + listStr.size());}//[start,end) 中是否有与 c[end] 相同的字符private static boolean isSwap(char[] c, int start, int end){for(int i = start; i < end; i++){if(c[i] == c[end])return true;}return false;}public static LinkedList<String> legalSequence(LinkedList<String> listStr){Iterator<String> it = listStr.iterator();String currentStr;while(it.hasNext())//检查全排列中的每个序列
        {currentStr = it.next();if(!check(currentStr))it.remove();//删除不符合的出栈规律的序列
        }return listStr;}//检查出栈序列 str 是否 是合法的出栈 序列private static boolean check(String str){boolean result = true;char[] c = str.toCharArray();char first;//当前数字.int k = 0;//记录 compare 数组中的元素个数char[] compare = new char[str.length()];for(int i = 0; i < c.length; i++){first = c[i];//找出在 first 之后的，并且比 first 小的数字for(int j = i+1; j < c.length; j++){if(c[j] > first)continue;else{compare[k++] = c[j];//将比当前数字小的 所有数字 放在compare数组中
                }}if(k == 0)continue;else{for(int m = 0; m < k-1; m++)//判断 compare 数组是否是 递减的顺序
                {if(compare[m] < compare[m+1]){result = false;//不符合递减顺序return result;}}}k=0;}return result;}//hapjin testpublic static void main(String[] args) {String str = "1234";LinkedList<String> listStr = legalSequence(allPermutation(str));print(listStr);}
}