[LeetCode] 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?

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