Fibonacci Number
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,
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| F(0) = 0, F(1) = 1
F(N) = F(N - 1) + F(N - 2), for N > 1.
Given N, calculate F(N).
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| Eample 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.
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Java Solution:
recursion
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| public int fib(int N) {
if(N == 0){
return 0;
}
else if(N == 1){
return 1;
}
return fib(N-1) + fib(N-2);
}
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iteration
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| public int fib(int N) {
int fib_0 = 0;
int fib_1 = 1;
int ret = 0;
if(N == 0) return fib_0;
if(N == 1) return fib_1;
for(int i = 1; i < N;i++){
//fib(N) = fib(N-1) + fib(N-2)
int left = fib_0;
int right = fib_1;
ret = left + right;
fib_0 = right;
fib_1 = ret;
}
return ret;
}
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