2.Add Two Numbers

题目：

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.

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

实现：

#include <stdio.h>
#include <stdlib.h>

struct ListNode {
    int val;
    struct ListNode *next;
};

void traverseList(struct ListNode *headNode);
struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2);

int main(int argc, const char * argv[]) {
    struct ListNode *node_1 = malloc(sizeof(struct ListNode));
    node_1->val = 5;
    node_1->next = NULL;

    struct ListNode *node_4 = malloc(sizeof(struct ListNode));
    node_4->val = 5;
    node_4->next = NULL;
    
    traverseList(node_1);
    traverseList(node_4);
    
    struct ListNode *resultNode = addTwoNumbers(node_1, node_4);
    traverseList(resultNode);

    return 0;
}

struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
    //结构指针,首地址指针
    struct ListNode *resultNode = malloc(sizeof(struct ListNode));
    resultNode->val = 0;
    resultNode->next = NULL;
    
    //用来存放进位值
    int carryNum = 0;
    //遍历指针
    struct ListNode *p1 = l1, *p2 = l2, *p3 = resultNode;
    //循环处理O(n)
    while (p1 != NULL || p2 != NULL) {
        if (NULL != p1) {
            carryNum += p1->val;
            p1 = p1->next;
        }
        
        if (NULL != p2) {
            carryNum += p2->val;
            p2 = p2->next;
        }
        p3->next = malloc(sizeof(struct ListNode));
        p3 = p3->next;
        p3->val = carryNum % 10;
        p3->next = NULL;
        carryNum /= 10;
    }
    
    if (0 != carryNum) {
        p3->next = malloc(sizeof(struct ListNode));
        p3 = p3->next;
        p3->val = carryNum % 10;
        p3->next = NULL;
    }
    
    return resultNode->next;
}


/**
 遍历单链表

 @param headNode 单链表头结点指针
 */
void traverseList(struct ListNode *headNode) {
    //游标指针
    struct ListNode *p = headNode;
    while (NULL != p) {
        if (NULL != p->next) {
            printf("%d->",p->val);
        }else {
            printf("%d",p->val);
        }
        p = p->next;
    }
    printf("\n");
}