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* style: insert newline at eof * style: use `InsertNewlineAtEOF` in `clang-format` * fix: use `clang-format-16` * chore: update clang-format-lint-action to v0.16.2 --------- Co-authored-by: Debasish Biswas <debasishbsws.dev@gmail.com>
113 lines
3.5 KiB
Java
113 lines
3.5 KiB
Java
package com.thealgorithms.dynamicprogramming;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Scanner;
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/**
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* @author Varun Upadhyay (https://github.com/varunu28)
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*/
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public class Fibonacci {
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private static Map<Integer, Integer> map = new HashMap<>();
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public static void main(String[] args) {
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// Methods all returning [0, 1, 1, 2, 3, 5, ...] for n = [0, 1, 2, 3, 4, 5, ...]
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Scanner sc = new Scanner(System.in);
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int n = sc.nextInt();
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System.out.println(fibMemo(n));
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System.out.println(fibBotUp(n));
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System.out.println(fibOptimized(n));
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System.out.println(fibBinet(n));
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sc.close();
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}
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/**
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* This method finds the nth fibonacci number using memoization technique
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*
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* @param n The input n for which we have to determine the fibonacci number
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* Outputs the nth fibonacci number
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*/
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public static int fibMemo(int n) {
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if (map.containsKey(n)) {
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return map.get(n);
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}
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int f;
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if (n <= 1) {
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f = n;
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} else {
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f = fibMemo(n - 1) + fibMemo(n - 2);
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map.put(n, f);
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}
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return f;
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}
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/**
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* This method finds the nth fibonacci number using bottom up
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*
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* @param n The input n for which we have to determine the fibonacci number
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* Outputs the nth fibonacci number
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*/
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public static int fibBotUp(int n) {
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Map<Integer, Integer> fib = new HashMap<>();
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for (int i = 0; i <= n; i++) {
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int f;
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if (i <= 1) {
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f = i;
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} else {
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f = fib.get(i - 1) + fib.get(i - 2);
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}
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fib.put(i, f);
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}
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return fib.get(n);
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}
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/**
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* This method finds the nth fibonacci number using bottom up
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*
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* @param n The input n for which we have to determine the fibonacci number
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* Outputs the nth fibonacci number
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* <p>
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* This is optimized version of Fibonacci Program. Without using Hashmap and
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* recursion. It saves both memory and time. Space Complexity will be O(1)
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* Time Complexity will be O(n)
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* <p>
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* Whereas , the above functions will take O(n) Space.
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* @author Shoaib Rayeen (https://github.com/shoaibrayeen)
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*/
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public static int fibOptimized(int n) {
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if (n == 0) {
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return 0;
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}
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int prev = 0, res = 1, next;
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for (int i = 2; i <= n; i++) {
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next = prev + res;
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prev = res;
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res = next;
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}
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return res;
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}
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/**
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* We have only defined the nth Fibonacci number in terms of the two before it. Now, we will
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* look at Binet's formula to calculate the nth Fibonacci number in constant time. The Fibonacci
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* terms maintain a ratio called golden ratio denoted by Φ, the Greek character pronounced
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* ‘phi'. First, let's look at how the golden ratio is calculated: Φ = ( 1 + √5 )/2
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* = 1.6180339887... Now, let's look at Binet's formula: Sn = Φⁿ–(– Φ⁻ⁿ)/√5 We first calculate
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* the squareRootof5 and phi and store them in variables. Later, we apply Binet's formula to get
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* the required term. Time Complexity will be O(1)
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*/
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public static int fibBinet(int n) {
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double squareRootOf5 = Math.sqrt(5);
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double phi = (1 + squareRootOf5) / 2;
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int nthTerm = (int) ((Math.pow(phi, n) - Math.pow(-phi, -n)) / squareRootOf5);
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return nthTerm;
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}
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}
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