51 lines
1.2 KiB
C++
51 lines
1.2 KiB
C++
// Source : https://leetcode.com/problems/fibonacci-number/
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// Author : Hao Chen
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// Date : 2019-03-26
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/*****************************************************************************************************
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*
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* The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such
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* that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
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*
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* F(0) = 0, F(1) = 1
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* F(N) = F(N - 1) + F(N - 2), for N > 1.
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*
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* Given N, calculate F(N).
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*
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* Example 1:
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*
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* Input: 2
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* Output: 1
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* Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
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*
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* Example 2:
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*
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* Input: 3
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* Output: 2
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* Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
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*
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* Example 3:
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*
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* Input: 4
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* Output: 3
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* Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
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*
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* Note:
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*
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* 0 ≤ N ≤ 30.
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******************************************************************************************************/
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class Solution {
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public:
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int fib(int N) {
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if (N < 2 ) return N;
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int first = 0, second = 1;
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for ( N-=1; N > 0; N-- ) {
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second += first;
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first = second - first;
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}
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return second;
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}
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};
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