Leetcode/ClimbingStairs.java at master · Jinglin-LI/Leetcode · GitHub

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/*
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?
*/

class Solution {
    public int climbStairs(int n) {
        if (n <= 2)
            return n;

        int[] dp = new int[n];
        dp[0] = 1;
        dp[1] = 2;
        for (int i = 2; i < n; i++) {
            dp[i] = dp[i - 1] + dp[i - 2];
        }
        return dp[n - 1];
    }
}

/************************************************************************************************/

public class Solution {
    public int climbStairs(int n) {
        int p = 1;
        int q = 1;
        int temp = 1;

        for (int i = 2; i <= n; i++) {
            temp = q;
            q = p + q;
            p = temp;
        }
        return q;
    }
}