Problem
The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
F(0) = 0, F(1) = 1
F(N) = F(N - 1) + F(N - 2), for N > 1.
Given N, calculate F(N).
Example 1:
Input: 2
Output: 1
Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
Example 2:
Input: 3
Output: 2
Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
Example 3:
Input: 4
Output: 3
Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
Notes
DP Problem.
Important:
Note how long is the dp array. It shoud be N+1, since we start with the number 0.
Solution
class Solution(object):
def fib(self, N):
"""
:type N: int
:rtype: int
"""
if N < 2:
return N
dp = [0] * (N + 1)
dp[0] = 0
dp[1] = 1
for i in range(2, N + 1):
dp[i] = dp[i - 1] + dp[i - 2]
return dp[-1]