11. Program to check whether a string is a palindrome or not.
public class P11_Palindrome {
public static void main(String[] args) {
String input = "level";
String reverse = "";
int flag = 0;
// Approach 1
for (int j = input.length() - 1; j >= 0; j--) {
reverse = reverse + input.charAt(j);
}
if (input.equals(reverse)) {
System.out.println("String : " + input + " is a palindrome");
} else {
System.out.println("String : " + input + " is not a palindrome");
}
// Approach 2
for (int i = 0; i < input.length(); i++) {
if (input.charAt(i) != input.charAt(input.length() - 1 - i)) {
flag++;
}
}
if (flag == 0) {
System.out.println("String : " + input + " is a palindrome");
} else {
System.out.println("String : " + input + " is not a palindrome");
}
}
}12. Program to check whether an integer is a palindrome or not.
public class P12_IntegerPalindrome {
public static void main(String[] args) {
int input = 4552554;
int num = input;
int reversedNum = 0;
int lastDigit = 0;
while(num > 0) {
lastDigit = num%10;
num = num/10;
reversedNum = reversedNum * 10 + lastDigit;
}
if (input == reversedNum) {
System.out.println("Number : " + input + " is a palindrome");
} else {
System.out.println("Number : " + input + " is not a palindrome");
}
}
}
13. Program to check whether two strings are string anagram or not.
import java.util.Arrays;
public class P13_StringAnagram {
public static void main(String[] args) {
String sInput1 = "Triangle";
String sInput2 = "Integral";
//check for string length
if(sInput1.length() != sInput2.length()) {
System.out.println(sInput1 + " and " + sInput2 + " are not anagrams");
} else {
//converting string to lowercase for comparision as anagrams are not case sensitive
//converting it later to char array
char[] sArray1 = sInput1.toLowerCase().toCharArray();
char[] sArray2 = sInput2.toLowerCase().toCharArray();
//sort the arrays so its arranged from a-z sequentially
Arrays.sort(sArray1);
Arrays.sort(sArray2);
//equals will check for length of two array
//It will also check if arrays are equal i.e, each character is same or not
if(Arrays.equals(sArray1, sArray2)) {
System.out.println(sInput1 + " and " + sInput2 + " are anagrams");
} else {
System.out.println(sInput1 + " and " + sInput2 + " are not anagrams");
}
}
}
}
14. Program to show how a string is immutable in nature.
public class P14_StringIsImmutable {
public static void main(String[] args) {
// New object is created with string "Two" as assignment is done
// input1 is assigned the address of new object that it is pointing to correctly
// existing object does not change
String input1 = "One";
input1 = "Two";
System.out.print("Output 1 : ");
System.out.println(input1);
// New object is created with string "An Apple a day, keeps doctor away!"
// Since assignment is not done, it is still pointing to the old object
// existing object does not change
String input2 = "An Apple";
input2.concat(" a day, keeps doctor away!");
System.out.print("Output 2 : ");
System.out.println(input2);
// New object is not created, it picks up existing object with string "An Apple a day, keeps doctor away!"
// input1 is assigned the address of new object that it is pointing to correctly
// existing object does not change
String input3 = "An Apple";
input3 = input3.concat(" a day, keeps doctor away!");
System.out.print("Output 3 : ");
System.out.println(input3);
// New object is created with string "Winter is here!" as
// assignment is done
// input1 is assigned the address of new object that it is pointing to correctly
// existing object does not change
String input4 = "Winter";
input4 = input4 + " is here!";
System.out.print("Output 4 : ");
System.out.println(input4);
}
}
15. Program to find duplicate characters in a string.
public class P15_DuplicateInAString {
public static void main(String[] args) {
String inputString = "Love your self";
char[] inputArray = inputString.toCharArray();
char[] outputArray = new char[inputString.length()];
int flag = 0;
int index = 0;
outer: for(char c_outer: inputArray) {
//To check for every character of outer array
flag = 0;
for(char c_inner: inputArray) {
//check if it matches a character and its not space
//set flag to indicate duplicate exists
if(c_outer == c_inner && c_outer != ' ') {
flag++;
}
}
if(flag > 1) {
//duplicate exists
//check if value is already present in output array
for(int i=0; i<outputArray.length; i++) {
if(c_outer == outputArray[i]) {
continue outer;
}
}
//set duplicate entry in output array
outputArray[index] = c_outer;
index++;
}
}
System.out.println("Duplicates in String '" + inputString + "' are - ");
for(int i = 0; i < outputArray.length; i++) {
//As length of output array is equal to input array, so remaining values will be zero
if(outputArray[i] != 0) {
System.out.println(outputArray[i]);
}
}
}
}
16. Program to find duplicate characters in a string using a HashMap.
import java.util.HashMap;
import java.util.Map;
public class P16_DuplicateInAStringUsingMap {
public static void main(String[] args) {
String input = "Programming";
Map<Character, Integer> output = new HashMap<Character, Integer>();
char[] characters = input.toCharArray();
for(char c: characters) {
if(output.containsKey(c)) {
output.put(c, output.get(c)+1);
} else {
output.put(c, 1);
}
}
for(char c_o : output.keySet()) {
if(output.get(c_o)>1) {
System.out.println("Character: " + c_o + " Count: " + output.get(c_o));
}
}
}
}
17. Program to remove duplicates from an ArrayList.
import java.util.ArrayList;
import java.util.LinkedHashSet;
public class P17_RemoveDuplicateFromArrayList {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<String>();
list.add("Two");
list.add("One");
list.add("Three");
list.add("Four");
list.add("Three");
list.add("Two");
list.add("Five");
list.add("Two");
LinkedHashSet<String> newList = new LinkedHashSet<String>(list);
list.clear();
list.addAll(newList);
System.out.println(list);
}
}
18. Program to print a triangle of stars.
public class P18_PrintTriangleOfStars {
public static void main(String[] args) {
int n = 5;
for(int i=0; i< n; i++) {
for(int j=0;j<i+1;j++) {
System.out.print("*");
}
System.out.println("");
}
}
}
19. Program to print a pyramid of stars.
public class P19_PrintPyramidOfStars {
public static void main(String[] args) {
int lines = 5;
int spaces = lines - 1;
int stars = 1;
for(int i=0; i< lines; i++) {
stars = (i*2)+1;
//print spaces
for(int k=spaces; k>0;k--) {
System.out.print(" ");
}
//print stars
for(int j=0;j<stars;j++) {
System.out.print("*");
}
System.out.println("");
spaces--;
}
}
}
20. Program to find the square root of a number.
public class P20_SquareRootOfNumber {
public static void main(String[] args) {
SquareRootOfNumber sqrt = new SquareRootOfNumber();
int num = 16;
//default method
System.out.println(Math.sqrt(num));
//custom approach
//prints only if perfect sqrt present
for(int i=1; i< num/2; i++) {
if(num/i == i && num%i == 0) {
System.out.println(i);
break;
}
}
}
}