# Problem

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

# Java 实现

``````
package com.coderli.leetcode.algorithms.easy;

/**
* ou are climbing a stair case. It takes n steps to reach to the top.
* <p>
* Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
* <p>
* Note: Given n will be a positive integer.
* <p>
* <p>
* Example 1:
* <p>
* Input: 2
* Output:  2
* Explanation:  There are two ways to climb to the top.
* <p>
* 1. 1 step + 1 step
* 2. 2 steps
* Example 2:
* <p>
* Input: 3
* Output:  3
* Explanation:  There are three ways to climb to the top.
* <p>
* 1. 1 step + 1 step + 1 step
* 2. 1 step + 2 steps
* 3. 2 steps + 1 step
*
* @author OneCoder 2017-11-08 22:03
*/
public class ClimbingStairs {

public static void main(String[] args) {
String s = "a" + "b" + "c" + "d";
ClimbingStairs climbingStairs = new ClimbingStairs();
System.out.println(climbingStairs.climbStairsWithRecursion(3));
System.out.println(climbingStairs.climbStairsWithRecursion(10));
System.out.println(climbingStairs.climbStairsWithRecursion(44));
System.out.println(climbingStairs.climbStairs(44));
}

public int climbStairsWithRecursion(int n) {
if (n == 1) {
return 1;
} else if (n == 2) {
return 2;
} else {
return climbStairsWithRecursion(n - 1) + climbStairsWithRecursion(n - 2);
}
}

public int climbStairs(int n) {
if (n == 1) {
return 1;
}
int prev = 1;
int cur = 2;
for (int i = 3; i <= n; i++) {
int temp = cur;
cur += prev;
prev = temp;
}
return cur;
}
}

``````

Thanks a lot.