Java

climbingStars.java

/*
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?
*/

//DP Solution


public class Solution {
    public int climbStairs(int n) {
        if (n<0){
            return 0;
        }
        
        // record unique ways for each n
        int [] unique_ways=new int[n+1];
        // start point which contains only one situation
        unique_ways[0]=1;
        
        // can only move 1 step , so ways is only 1
        unique_ways[1]=1;
        
        for (int i=2; i<n+1; i++){
            unique_ways[i]=unique_ways[i-1]+unique_ways[i-2];
        }
        
        return unique_ways[n];
    }
}