【LeetCode】Climbing Stairs

http://oj.leetcode.com/problems/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?

递归解法

public class Solution {
    public int climbStairs(int n) {
        if(n==0)
            return 0;
        if(n==1)
            return 1;
        if(n==2)
            return 2;
        
        return FClimbStairs(n);
        
    }

  
    
    private int FClimbStairs(int n) {
        // TODO Auto-generated method stub
        if(n==1)
            return 1;
        if(n==2)
            return 2;
        
        return FClimbStairs(n-1)+FClimbStairs(n-2);
    }
}

非递归解法

public class Solution {
    public int climbStairs(int n) {
        if(n==0)
            return 0;
        if(n==1)
            return 1;
        if(n==2)
            return 2;
        int[] re = new int[n+1];
        re[0]=0;
        re[1]=1;
        re[2]=2;
        for(int i=3;i<n+1;i++){
            re[i]=re[i-1]+re[i-2];
        }
        return re[n];
        
    }

    
}