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: 2Output: 2Explanation: There are two ways to climb to the top.1. 1 step + 1 step2. 2 stepsExample 2:Input: 3Output: 3Explanation: There are three ways to climb to the top.1. 1 step + 1 step + 1 step2. 1 step + 2 steps3. 2 steps + 1 step难度：easy题目：爬楼梯用例。要用n 步才能到达顶端.第次可以爬1或2步，有多少种爬上楼顶的方式？注意：n是正整数。思路：递归转迭代Runtime: 2 ms, faster than 100.00% of Java online submissions for Climbing Stairs.Memory Usage: 25.4 MB, less than 93.69% of Java online submissions for Climbing Stairs.public class Solution { public int climbStairs(int n) { if (n <= 1) { return 1; } int num1 = 1, num2 = 1, result = num1 + num2; for (int i = 1; i < n; i++) { result = num1 + num2; num1 = num2; num2 = result; } return result; }}