70. Climbing Stairs, 70 climbingstairs

70. Climbing Stairs, 70 climbingstairs

You are climbing a stair case. It takesNSteps 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?

The recursive formula is f (n) = f (n-1) + f (n-2)

Each element only depends on the first two elements.

 

1 class Solution {2 public: 3 int climbStairs (int n) {4 int result [3] = {0, 1, 2}; 5 if (n <3) {6 return result [n]; 7} 8 9 int f1 = 1; 10 int f2 = 2; 11 int fn = 0; 12 13 for (int I = 3; I <= n; I ++) {14 fn = f1 + f2; 15 f1 = f2; 16 f2 = fn; 17} 18 return fn; 19} 20 };