A child is running up a staircase with n steps and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a method to count how many possible ways the child can run up the stairs.
public static int getPossibleWays(final int n) { int[] memo = new int[n + 1]; return helper(n, memo); } private static int helper(int i, int[] memo) { if(i == 0 || i == 1) return 1; if(i ==2) return 2; if(i >=3 && memo[i] == 0) { memo[i] = helper(i -1, memo) + helper(i -2, memo) + helper(i -3, memo); } return memo[i]; }
原文：http://www.cnblogs.com/Phoebe815/p/6143496.html