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April 14, 2018 18:13
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Different methods to compute nth Fibonacci number
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/* File: NumberOfSubsetsWithTargetSum.java | |
* Created: 2017-04-13 | |
* Author: Sabbir Manandhar | |
* | |
* Copyright (c) 2017 manandharsabbirk.appspot.com | |
*/ | |
/** | |
* Computes Number of Sub-sets that have sums to targetSUm | |
* | |
* @author Sabbir Manandhar manandhar.sabbir@gmail.com | |
* @version 1.0 | |
*/ | |
public class Fibonacci { | |
/** | |
* main method | |
*/ | |
public static void main(String[] args) { | |
int n = 50; | |
long now = System.currentTimeMillis(); | |
System.out.println(fib_memoization(n, new long[n+1])); | |
System.out.println("Computed with Memoization in: " + (System.currentTimeMillis()-now)); | |
now = System.currentTimeMillis(); | |
//System.out.println(fib_recursion(n)); | |
System.out.println("Computed with Recursion in: " + (System.currentTimeMillis()-now)); | |
now = System.currentTimeMillis(); | |
System.out.println(fib_dp(n)); | |
System.out.println("Computed with DP in: " + (System.currentTimeMillis()-now)); | |
now = System.currentTimeMillis(); | |
System.out.println(fib_dp_modified(n)); | |
System.out.println("Computed with modified DP in: " + (System.currentTimeMillis()-now)); | |
} // main | |
//-------------------------------------------------------------------------- | |
/** | |
* Compute nth Fibonacci number using Recursion | |
*/ | |
public static long fib_recursion(int n) { | |
if (n == 0) { | |
return 0; | |
} | |
if (n == 1) { | |
return 1; | |
} | |
return fib_recursion(n-2) + fib_recursion(n-1); | |
} // fib | |
//-------------------------------------------------------------------------- | |
/** | |
* Compute nth Fibonacci number using memoization | |
*/ | |
public static long fib_memoization(int n, long[] mem) { | |
if (n == 0 || n == 1) { | |
mem[n] = n; | |
return n; | |
} | |
if (mem[n] == 0) { | |
mem[n] = fib_memoization(n-2, mem) + fib_memoization(n-1, mem); | |
} | |
return mem[n]; | |
} // fib | |
//-------------------------------------------------------------------------- | |
/** | |
* Compute nth Fibonacci number using DP | |
*/ | |
public static long fib_dp(int n) { | |
long[] dp = new long[n+1]; | |
for (int i = 0; i <= n; i++) { | |
if (i == 0 || i == 1) { | |
dp[i] = i; | |
continue; | |
} | |
dp[i] = dp[i-1] + dp[i-2]; | |
} | |
return dp[n]; | |
} // fib3 | |
//-------------------------------------------------------------------------- | |
/** | |
* Compute nth Fibonacci number using modified DP | |
*/ | |
public static long fib_dp_modified(int n) { | |
if (n == 0 || n == 1) { | |
return n; | |
} | |
long first = 0; | |
long second = 1; | |
int k = 2; | |
do { | |
long temp = first + second; | |
first = second; | |
second = temp; | |
if (k == n) { | |
return second; | |
} | |
k++; | |
} while (true); | |
} // fib4 | |
//-------------------------------------------------------------------------- | |
} // Fibonacci |
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