leetcode: 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?

class Solution {
public:
int climbStairs(int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (n == 0)
return 0;
if (n == 1)
return 1;
if (n == 2)
return 2;

int curStep;
int preStep     = 2;
int preTwoStep  = 1;

for (int i=3; i<=n; i++)
{
curStep    = preStep + preTwoStep;
preTwoStep = preStep;
preStep    = curStep;
}

return curStep;
}
};