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FibonacciNumber.java
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FibonacciNumber.java
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package Leetcode;
/**
* @author kalpak
*
* 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: n = 2
* Output: 1
* Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
*
*
* Example 2:
* Input: n = 3
* Output: 2
* Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
*
*
* Example 3:
* Input: n = 4
* Output: 3
* Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
*
*
* Constraints:
*
* 0 <= n <= 30
*
*/
public class FibonacciNumber {
public static int fib(int n) {
int[] dp = new int[n + 1];
return computeFibonacciTopDown(dp, n);
}
private static int computeFibonacciTopDown(int[] dp, int n) {
if (n < 2)
return n;
if(dp[n] == 0)
dp[n] = computeFibonacciTopDown(dp, n - 1) + computeFibonacciTopDown(dp, n - 2);
return dp[n];
}
public static int computeFibonacciBottomsUp(int n) {
if(n < 2)
return n;
int[] dp = new int[n + 1];
dp[0] = 0;
dp[1] = 1;
for(int i = 2; i <= n; i++) {
dp[i] = dp[i - 1] + dp[i - 2];
}
return dp[n];
}
public static int computeFibonacciBottomsUpOptimized(int n) {
if(n < 2)
return n;
int num1 = 0;
int num2 = 1;
int temp = 0;
for(int i = 2; i <= n; i++) {
temp = num1 + num2;
num1 = num2;
num2 = temp;
}
return temp;
}
public static void main(String[] args) {
System.out.println(fib(12));
System.out.println(computeFibonacciBottomsUp(12));
System.out.println(computeFibonacciBottomsUpOptimized(12));
}
}