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Recursion.java
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Recursion.java
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public class RecursionBasics {
public static void printDec(int n) {
if(n == 1) {
System.out.println(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 fact(int n) {
if(n == 0) {
return 1;
}
int fnm1 = fact(n-1);
int fn = n * fact(n-1);
return fn;
}
public static int calcSum(int n) {
if(n == 1) {
return 1;
}
int Snm1 = calcSum(n-1);
int Sn = n + Snm1;
return Sn;
}
//calculate nth term in fibonacci
public static int fib(int n) {
if(n == 0 || n == 1) {
return n;
}
int fnm1 = fib(n-1);
int fnm2 = fib(n-2);
int fn = fnm1 + fnm2;
return fn;
}
public static boolean isSorted(int arr[], int i) {
if(i == arr.length-1) {
return true;
}
if(arr[i] > arr[i+1]) {
return false;
}
return isSorted(arr, i+1);
}
public static int firstOccurence(int arr[], int key, int i) {
if(i == arr.length) {
return -1;
}
if(arr[i] == key) {
return i;
}
return firstOccurence(arr, key, i+1);
}
public static int lastOccurence(int arr[], int key, int i) {
if(i == arr.length) {
return -1;
}
int isFound = lastOccurence(arr, key, i+1);
if(isFound == -1 && arr[i] == key) {
return i;
}
return isFound;
}
public static int power(int x, int n) {
if(n == 0) {
return 1;
}
// int xnm1 = power(x, n-1);
// int xn = x * xnm1;
// return xn;
return x * power(x, n-1);
}
public static int optimizedPower(int x, int n) {
if(n == 0) {
return 1;
}
if(n % 2 == 0) { //even
return optimizedPower(x, n/2) * optimizedPower(x, n/2);
} else { //odd
return x * optimizedPower(x, n/2) * optimizedPower(x, n/2);
}
}
public static int tilingProblem(int n) { // 2 x n (floor size)
//base case
if(n == 0 || n == 1) {
return 1;
}
//kaam
//vertical choice
int fnm1 = tilingProblem(n-1);
//horizontal choice
int fnm2 = tilingProblem(n-2);
int totWays = fnm1 + fnm2;
return totWays;
}
public static void removeDuplicates(String str, int idx, StringBuilder newStr, boolean map[]) {
if(idx == str.length()) {
System.out.println(newStr);
return;
}
//kaam
char currChar = str.charAt(idx);
if(map[currChar-'a'] == true) {
//duplicate
removeDuplicates(str, idx+1, newStr, map);
} else {
map[currChar-'a'] = true;
removeDuplicates(str, idx+1, newStr.append(currChar), map);
}
}
public static int friendsPairing(int n) {
if(n == 1 || n == 2) {
return n;
}
return friendsPairing(n-1) + (n-1) * friendsPairing(n-2);
}
public static void printBinStrings(int n, int lastPlace, String str) {
//base case
if(n == 0) {
System.out.println(str);
return;
}
//kaam
printBinStrings(n-1, 0, str+"0");
if(lastPlace == 0) {
printBinStrings(n-1, 1, str+"1");
}
}
public static void main(String args[]) {
printBinStrings(3, 0, "");
}
}