70. Climbing Stairs

题目

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

解析

// add 70. Climbing Stairs
class Solution_70 {
public:
    int climbStairs(int n) {

        int ret = 0;
        int f1 = 1, f2 = 2;

        if (n == 1 || n == 2)
        {
            return n;
        }
        for (int i = 3; i <= n;i++)
        {
            int temp = f1 + f2;
            f1 = f2;
            f2 = temp;
        }
        return f2;
    }


    int climbStairs_(int n)
    {
        if (n==1||n==2)
        {
            return  n;
        }
        return climbStairs_(n - 1) + climbStairs_(n - 2);
    }

};

题目来源

• 70. Climbing Stairs