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Recursion.java
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Recursion.java
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import java.security.spec.RSAOtherPrimeInfo;
public class Recursion {
public static void printdec(int n){
if (n==1){
System.out.print(n + " ");
return;
}
System.out.print(n + " ");
printdec(n-1);
}
public static void printInc(int n){
if (n==1){
System.out.print(n + " ");
return;
}
printInc(n-1);
System.out.print(n + " ");
}
public static int factorial(int n){
if (n==0){
return 1;
}
int ans = n * factorial(n-1);
return ans;
}
public static int sumN_Natural(int n){
if (n==1){
return 1;
}
int sum = n + sumN_Natural(n-1);
return sum;
}
public static int nth_fibonacci(int n){
if (n==1 || n==0){
return n;
}
int ans = nth_fibonacci(n-1) + nth_fibonacci(n-2);
return ans;
}
public static void fibonacci(int n){
int n1=0,n2=1,n3,i,count=10;
System.out.print(n1+" "+n2);
for(i=2;i<count;++i)
{
n3=n1+n2;
System.out.print(" "+n3);
n1=n2;
n2=n3;
}
}
public static int fibonacci_with_recursion(int n){
if (n==1 || n==0){
return n;
}
int ans = fibonacci_with_recursion(n-1) + fibonacci_with_recursion(n-2);
return ans;
}
public static boolean isSortedArray(int[] arr, int i){
if (i==arr.length-1){
return true;
}
if (arr[i] > arr[i+1]){
return false;
}
return isSortedArray(arr, i+1);
}
public static int first_Occurence(int[] arr, int key, int i){
if (i == arr.length) return -1;
if (arr[i] == key) return i;
return first_Occurence(arr, key, i+1);
}
public static int last_Occurence(int[] arr, int key, int i){
if (i == arr.length) return -1;
int index = last_Occurence(arr, key, i+1);
if (index == -1 && arr[i] == key){
return i;
}
return index;
}
public static int pow(int x, int n){
if (n==0) return 1;
int xn = x * pow(x, n-1);
return xn;
}
public static int pow_optimized(int x, int n){
if (n==0) return 1;
int a = pow(x, n/2);
if (n%2 == 0){
return a*a;
}else {
return x * a * a;
}
// if (n%2 == 0) return pow(x, n/2) * pow(x, n/2); // do not call twice as time complexity is still the same
// else return x * pow(x, n/2) * pow(x, n/2); // do not call twice as time complexity is still the same
}
public static int facto(int n){
if (n==0 || n==1) return 1;
return n * facto(n-1);
}
public static void main(String[] args) {
printInc(10);
System.out.println();
printdec(10);
System.out.println("\n" + factorial(5));
System.out.println(sumN_Natural(5));
System.out.println(nth_fibonacci(5));
fibonacci(10);
System.out.println();
// int n = 10;
// System.out.print(0 + " " + 1);
// fibonacci_with_recursion(n-2);
int n = 10;
for (int i=0; i<n; i++){
System.out.print(fibonacci_with_recursion(i) + " ");
}
System.out.println();
int[] arr = {1, 1, 2, 9};
System.out.println(isSortedArray(arr,0));
int[] nums = {8, 3, 6, 9, 5, 10, 2, 5, 3, 5};
int index = first_Occurence(nums, 5, 0);
System.out.println(index);
int[] arr2 = {5, 2, 1, 2, 4, 2};
System.out.println(last_Occurence(arr2, 2, 0));
System.out.println(facto(3));
System.out.println(pow(2,4));
System.out.println(pow_optimized(2, 10));
}
}