爬楼梯的问题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?

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//类似于斐波那契数列
public class Solution {

public int climbStairs(int n) {

if(n <= 0) return 0;

if(n == 1) return 1;

if(n == 2) return 2;

int one_step_before = 2;

int two_steps_before = 1;

int all_ways = 0;

for(int i=2; i<n; i++){

all_ways = one_step_before + two_steps_before;

two_steps_before = one_step_before;

one_step_before = all_ways;

}

return all_ways;

}

}