Add Two Numbers

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算法：链表 Linked list

题目：Add Two Numbers

url：https://leetcode.com/problems/add-two-numbers/

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

分析

• 百位大数相加

Java解法

方法	定义
链表增加节点
单链表反转	不需要，只是为了练习算法
遍历链表

package com.test.demo;

import java.io.IOException;

class ListNode {
    int val;
    ListNode next;
    public ListNode(int x) {this.val = x;}
}

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    	ListNode retNode = null;
    	int carryBit = 0;
        while(l1 != null || l2!= null) {
        	int d1 = null==l1 ? 0 : l1.val;
        	int d2 = null==l2 ? 0 : l2.val;
        	int d = d1 + d2 + carryBit;
        	retNode = add(retNode, new ListNode(d%10));
        	carryBit = d/10;
        	l1 = null==l1 ? l1 : l1.next;
        	l2 = null==l2 ? l2 : l2.next;
        }
        for (int i = carryBit; i>0; i = i/10) {
        	retNode = add(retNode, new ListNode(i%10));
        }
        return retNode;
//        return reverse(retNode);
    }
    public ListNode add(ListNode headNode, ListNode node) {
    	if (null == headNode) {
    		headNode = node;
    	} else {
	        ListNode index = headNode;
	        while(index.next != null) {index = index.next;}
	        index.next = node;
    	}
        return headNode;
    }
    public ListNode reverse(ListNode headNode) {
        if(headNode == null) return headNode;
        ListNode pre = headNode;
        ListNode cur;
        ListNode temp;
        for(cur = headNode.next; cur!=null; ) {
        	temp = cur.next;
        	cur.next = pre; 
            pre = cur;
            cur = temp;
        }
        headNode.next = null;
        return pre;
    }
}

public class MainClass {
    public static int[] stringToIntegerArray(String input) {
        input = input.trim();
        input = input.substring(1, input.length() - 1);
        if (input.length() == 0) {
          return new int[0];
        }
    
        String[] parts = input.split(",");
        int[] output = new int[parts.length];
        for(int index = 0; index < parts.length; index++) {
            String part = parts[index].trim();
            output[index] = Integer.parseInt(part);
        }
        return output;
    }
    
    public static ListNode stringToListNode(String input) {
        // Generate array from the input
        int[] nodeValues = stringToIntegerArray(input);
    
        // Now convert that list into linked list
        ListNode dummyRoot = new ListNode(0);
        ListNode ptr = dummyRoot;
        for(int item : nodeValues) {
            ptr.next = new ListNode(item);
            ptr = ptr.next;
        }
        return dummyRoot.next;
    }
    
    public static String listNodeToString(ListNode node) {
        if (node == null) {
            return "[]";
        }
    
        String result = "";
        while (node != null) {
            result += Integer.toString(node.val) + ", ";
            node = node.next;
        }
        return "[" + result.substring(0, result.length() - 2) + "]";
    }
    
    public static void main(String[] args) throws IOException {

            ListNode l1 = stringToListNode("[9]");
            ListNode l2 = stringToListNode("[1,9,9,9,9,9,9,9,9,9]");
            
            ListNode ret = new Solution().addTwoNumbers(l1, l2);
            String out = listNodeToString(ret);
            
            System.out.print(out);
    }
}

Python解法

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