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.

程序代码：

int climbStairs(int n) {
    int TwoStep=1,OneStep=1,i,sum=0;
    if(n==1)
        sum = 1;
    for(i=2;i<=n;i++)
    {
        sum = TwoStep+OneStep;
        TwoStep = OneStep;
        OneStep= sum;
    }
    return sum;
}