70. 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.

本质上是dp计算Fibonacci数列：

class Solution {
public:
int climbStairs(int n) {
int* dp=(int*)malloc(sizeof(int)*(n+1));
dp[1]=1;
dp[2]=2;
for(int i=3;i<=n;i++)
dp[i]=dp[i-1]+dp[i-2];
return dp
;
}
};更快一些：

class Solution {
public:
int climbStairs(int n) {
if(n==1 || n==2)
return n;
int num1=1, num2=2;
for(int i=3; i<=n; i++)
{
int number = num1+num2;
num1=num2;
num2=number;
}
return num2;
}
};