Problem Description
You are climbing a staircase and it takes A steps to reach the top.
Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
Return the number of distinct ways modulo 1000000007
Solution
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public class Solution {
int M = 1000000007;
public int climbStairs(int A) {
int[] dp = new int[A+1];
dp[0] = 1;
dp[1] = 1;
return climbStairsHelper(A, dp);
}
public int climbStairsHelper(int N, int[] dp){
if(N == 0 || N == 1) return 1;
if(dp[N] == 0){
dp[N] = (climbStairsHelper(N-1, dp)%M + climbStairsHelper(N-2, dp)%M)%M;
}
return dp[N];
}
}