[LeetCode]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?

深搜+备忘录

public class Solution {
	int f[];
	public int climbStairs(int n) {
		f = new int[n+1];
		return climb(n);
	}
	
	private int climb(int n){
		if(n<=0) return 0;
		if(n==1) return 1;
		if(n==2) return 2;
		return store(n-1)+store(n-2);
	}
	
	private int store(int n){
		if(n<=0) return 0;
		if(f[n]>0) return f[n];
		return f[n] = climb(n);
	}
}

迭代法（比递归更优）

public class Solution {
	public int climbStairs(int n){
		int prev = 0;
		int cur = 1;
		for(int i=1;i<=n;i++){
			int temp = cur;
			cur += prev;
			prev = temp;
		}
		return cur;
	}
}