70. Climbing Stairs

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