LeetCode-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?

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

时间复杂度O(n)

public int climbStairs(int n) {//递推 斐波那契数 my
        int x1 = 0;
        int x2=1;
        int re = 0;
        for (int i = 1; i <= n; i++) {
            re = x1+x2;
            x1= x2;
            x2 =re;
        }
        return re;
    }　　

 也可使用递归，需保存中间结果以防止重复计算

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