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];    }};