## Leetcode 爬楼梯 (Climbing Stairs)

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?

Note: Given n will be a positive integer.

Example 1:

Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps


Example 2:

Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step


### 解法1

class Solution {
public:
int climbStairs(int n) {
if(n < 1){
return 0;
}
vector<int> temp(n+2,0);
int index = 0;
temp[index++] = 1;
temp[index++] = 1;
while (index <= n) {
temp[index] = temp[index -1 ]+temp[index-2];
index++;
}
return temp[n];
}
};


### 解法2

class Solution {
public:
int climbStairs(int n) {
if(n < 1){
return 0;
}
int a,b,c;
a = 1;
b = 0;
c = a+b;
int current = 1;
while (current <= n) {
a = b;
b = c;
c = a+b;
current ++;
}
return c;
}
};