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?

DP方法：

step[n] = step[n-1]+step[n-2];

class Solution {
public:
    int climbStairs(int n) {
        vector<int> step(n,0);
        step[0] = 1;
        step[1] = 2;
        for(int i = 2;i<n;i++){
            step[i] = step[i-1]+step[i-2];
        }
        return step[n-1];
    }
};