leetcode__Add Two Numbers && Climbing Stairs

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

总结：指针操作还是要多练习。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
        if(l2==NULL) return l1;
        if(l1==NULL) return l2;  

        ListNode *l3=NULL;
        ListNode *p = l3;
        int sum;
        int flag=0;
        while( l1 || l2 ){
            sum =  flag;
            if(l1){
                sum += l1->val;
                l1 = l1->next;
            }
            if(l2){
                sum += l2->val;
                l2 = l2->next;
            }  

            flag = sum /10;
            sum = sum%10;  

            if(!l3){
                l3 = new ListNode(sum);
                p  = l3;
            }else{
                p->next = new ListNode(sum);
                p = p->next;
            }
        }  

        if ( flag != 0){
            p->next = new ListNode(flag);
        }  

        return l3;
    }
};

Climbing Stairs

Total Accepted: 12531 Total
Submissions: 38495My Submissions

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

class Solution {
public:
    int climbStairs(int n) {
        int arr[200];
        int i;

        arr[0] = 1;
        arr[1] = 2;
        for(i=2;i<n;i++){
            arr[i] = arr[i-1] + arr[i-2];
        }

        return arr[n-1];
    }
};

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