25.復雜鏈表的復制

輸入一個復雜鏈表（每個節點中有節點值，以及兩個指針，一個指向下一個節點，另一個特殊指針指向任意一個節點），返回結果為復制後復雜鏈表的head。（註意，輸出結果中請不要返回參數中的節點引用，否則判題程序會直接返回空）

/*
public class RandomListNode {
    int label;
    RandomListNode next = null;
    RandomListNode random = null;

    RandomListNode(int label) {
        this.label = label;
    }
}
*/
public class Solution {
    public RandomListNode Clone(RandomListNode pHead)
    {
        //一定註意考慮輸入為空鏈表的情況
        if(pHead == null) return null;
        //第一步：克隆每個結點的值和next，並且將新節點放置在對應舊結點之後
        RandomListNode node = pHead;
        while(node != null){
            RandomListNode cloneNode = new RandomListNode(node.label);
            //cloneNode.label = node.label;
            cloneNode.next = node.next;
            node.next = cloneNode;
            node = cloneNode.next;
        }
        //第二步：克隆每個隨機指針
        node = pHead;
        while(node != null){
            RandomListNode cloneNode = node.next;
            if(node.random != null)
                cloneNode.random = node.random.next;
            node = cloneNode.next;
        }
        //第三步：拆分拼接的鏈表
        node = pHead;
        RandomListNode cloneHead = pHead.next;
        while(node != null){
            RandomListNode cloneNode = node.next;
            node.next = cloneNode.next;
            node = node.next;
            if(node != null)
                cloneNode.next = node.next;
            else
                cloneNode.next = null;
        }
        return cloneHead;
    } 
}
 

26.二叉搜索樹與雙向鏈表

輸入一棵二叉搜索樹，將該二叉搜索樹轉換成一個排序的雙向鏈表。要求不能創建任何新的結點，只能調整樹中結點指針的指向。

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public TreeNode Convert(TreeNode pRootOfTree) {
        if(pRootOfTree == null) return null;
        if(pRootOfTree.left == null && pRootOfTree.right == null) return pRootOfTree;
        TreeNode left = Convert(pRootOfTree.left);
        TreeNode node = left;
        
        if(node == null)
            pRootOfTree.left = null;
        else{
            while(node.right != null)
                node = node.right;
            pRootOfTree.left = node;
            node.right = pRootOfTree;
        }
        TreeNode right = Convert(pRootOfTree.right);
        pRootOfTree.right = right;
        if(right != null)
            right.left = pRootOfTree;
        return left != null ? left : pRootOfTree; 
    }
}
 

27.==字符串的排列==

題目描述
輸入一個字符串,按字典序打印出該字符串中字符的所有排列。例如輸入字符串abc,則打印出由字符a,b,c所能排列出來的所有字符串abc,acb,bac,bca,cab和cba。

輸入描述:
輸入一個字符串,長度不超過9(可能有字符重復),字符只包括大小寫字母。

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Collections;
public class Solution {
    ArrayList<String> result = new ArrayList<String>();
    public ArrayList<String> Permutation(String str) {
        if(str == null) return null;
        char[] charArray = str.toCharArray();
        permutation(charArray,0);
        Collections.sort(result);
        return result;
    }
    public void permutation(char[] charArray,int beginIdx){
        if(beginIdx >= charArray.length) return;
        if(beginIdx == charArray.length-1){
            result.add(String.valueOf(charArray));
        }
        HashSet<Character> charSet = new HashSet<>();
        for(int i = beginIdx;i<charArray.length;i++){
            if(i == beginIdx){
                charSet.add(charArray[i]);
                permutation(charArray,beginIdx+1);
            }else if(i != beginIdx && !charSet.contains(charArray[i])){
                char temp = charArray[beginIdx];
                charArray[beginIdx] = charArray[i];
                charArray[i] = temp;
                permutation(charArray,beginIdx+1);
                temp = charArray[beginIdx];
                charArray[beginIdx] = charArray[i];
                charArray[i] = temp;
            }
        }
    }
}
 

劍指offer第四天