These are some Java coding problems for practice, these could be helpful for interview preparation as well.
package test;
import java.util.ArrayList;
import java.util.Arrays;
public class PracticeVariousCodingExamples {
public static void main(String[] args) {
// Coding problems to practice:
//methods
//-------------------method 1----------------------------
//removeDuplicateChars();
//-------------------method 2----------------------------
//countRepetitionOfChars();
//-------------------method 3----------------------------
//findUniqueChars();
//-------------------method 4----------------------------
/* Palindrome:
System.out.println("is Palindrome ? true/false with static "+palindrome());//this proves that variable does not need to be static
2. without using static in the method and without using return
PracticeAll a = new PracticeAll();
a.palindrome();
System.out.println("is Palindrome ? true/false "+a.palindrome());
3. PracticeAll.Palindrome();//Method can be called this way also with class name or just call the method name like in 2 when static keyword is used in the method declaration. This is also without using 'return' keyword.
The method has been written in such a way that it can be called in the way mentioned in point 2 or point 3 only. Return keyword has not been used in out example here.
*/
//-------------------method 5----------------------------
//reformatGivenText(); //"bbbaadddddu"--> //3a-2b-4d-1u
//-------------------method 6----------------------------
//sumValueOfaString(); //find sum of the numerical values of each char from a given string
//-------------------method 7----------------------------
//sumTestfromArray();//find the array Elements from a given array whose sum equals a given number
//-------------------method 8----------------------------
//primeNum(); //prime number
//-------------------method 9----------------------------
//startingAndEndgingDigitSame(); //numbers having same starting and ending digits
//-------------------method 10----------------------------
//countUpperlower(); //Count upper case chars and lower case chars in a given string.
//-------------------method 11----------------------------
//Case statement in java
System.out.println(caseTest(2));
System.out.println(caseTest(3));
}
//-------------------method 1----------------------------
public static void removeDuplicateChars() {//show unique chars only
String str = "this is a beautiful world.";
String[] strArray = new String[str.length()];
for(int i=0;i<str.length();i++) {
strArray[i]= Character.toString(str.charAt(i));
}
System.out.println("Array1 = "+Arrays.toString(strArray));//[t, h, i, s, , i, s, , a, , b, e, a, u, t, i, f, u, l, , w, o, r, l, d, .]
Arrays.sort(strArray);
System.out.println("Array1 = "+Arrays.toString(strArray));//[ , , , , ., a, a, b, d, e, f, h, i, i, i, l, l, o, r, s, s, t, t, u, u, w]
ArrayList<String> alist = new ArrayList<>();
for(int i=1;i<str.length();i++) {
if(!(strArray[i-1].equals(strArray[i]))) {
alist.add(strArray[i]);
}
}
alist.add(strArray[strArray.length-1]);
System.out.println("unique chars = "+alist);//[., a, b, d, e, f, h, i, l, o, r, s, t, u, w, w]
}
//-------------------method 8----------------------------
public static void primeNum() {
// Find if the given number is a prime number or not. Return the smallest divisible number if not Prime Number OR return 1 if it is a Prime Number
int givenNumber = 17;
boolean isPrime = true;
int returnNum = 1;
for (int i = 2; i < givenNumber; i++) {
if ((givenNumber % i) == 0) {
isPrime = false;
returnNum = i;
break;
}
}
System.out.println("Is the number Prime ?"+isPrime + " The number returned is "+ returnNum);
}
//-------------------method 2----------------------------
public static void countRepetitionOfChars() {
String str = "helloworld.";
String[] strArray = new String[str.length()];
for(int i=0;i<str.length();i++) {
strArray[i]= Character.toString(str.charAt(i));
}
System.out.println("Array1 = "+Arrays.toString(strArray));//[h, e, l, l, o, w, o, r, l, d, .]
Arrays.sort(strArray);
System.out.println("Array1 = "+Arrays.toString(strArray));//[., d, e, h, l, l, l, o, o, r, w]
ArrayList<String> alist = new ArrayList<>();//unique chars
ArrayList<Integer> blist = new ArrayList<>();//index where the char changed
ArrayList<Integer> clist = new ArrayList<>();//count of each char
ArrayList<String> dlist = new ArrayList<>();//count of each char, number +char
for(int i=1;i<str.length();i++) {
if(!(strArray[i-1].equals(strArray[i]))) {
alist.add(strArray[i-1]);
}
}
alist.add(strArray[strArray.length-1]);
System.out.println("unique chars = "+alist);//[., d, e, h, l, o, r, w]
for(int i=1;i<str.length();i++) {
if(!(strArray[i-1].equals(strArray[i]))) {
blist.add(i-1);
}
}
blist.add(str.length()-1);
System.out.println("lower index where char changed = "+blist);//[0, 1, 2, 3, 6, 8, 9, 10]
clist.add(blist.get(0)+1);//imp
for(int i=1;i<blist.size();i++) {
clist.add(blist.get(i)-blist.get(i-1));
}
System.out.println("count of each char = "+clist);//[1, 1, 1, 1, 3, 2, 1, 1]
for(int i=0;i<blist.size();i++) {
dlist.add(alist.get(i).concat(Integer.toString(clist.get(i))));
}
System.out.println("Final Char with number = "+dlist);//[.1, d1, e1, h1, l3, o2, r1, w1]
}
//-------------------method 3----------------------------
public static void findUniqueChars() { //find chars which have no repetition.
String str = "helloworld.";
String[] strArray = new String[str.length()];
for(int i=0;i<str.length();i++) {
strArray[i]= Character.toString(str.charAt(i));
}
System.out.println("Array1 = "+Arrays.toString(strArray));//[h, e, l, l, o, w, o, r, l, d, .]
Arrays.sort(strArray);
System.out.println("Array1 = "+Arrays.toString(strArray));//[., d, e, h, l, l, l, o, o, r, w]
ArrayList<String> alist = new ArrayList<>();//unique chars
ArrayList<Integer> blist = new ArrayList<>();//index where the char changed
ArrayList<Integer> clist = new ArrayList<>();//count of each char
ArrayList<String> dlist = new ArrayList<>();//unique Char
for(int i=1;i<str.length();i++) {
if(!(strArray[i-1].equals(strArray[i]))) {
alist.add(strArray[i-1]);
}
}
alist.add(strArray[strArray.length-1]);
System.out.println("unique chars = "+alist);//[., d, e, h, l, o, r, w]
for(int i=1;i<str.length();i++) {
if(!(strArray[i-1].equals(strArray[i]))) {
blist.add(i-1);
}
}
blist.add(str.length()-1);
System.out.println("lower index where char changed = "+blist);//[0, 1, 2, 3, 6, 8, 9, 10]
clist.add(blist.get(0)+1);//imp
for(int i=1;i<blist.size();i++) {
clist.add(blist.get(i)-blist.get(i-1));
}
System.out.println("count of each char = "+clist);//[1, 1, 1, 1, 3, 2, 1, 1]
for(int i=0;i<blist.size();i++) {
if(clist.get(i)==1) {
dlist.add(alist.get(i));
}
}
System.out.println("unique chars = "+dlist);//[., d, e, h, r, w]
}
//-------------------method 4----------------------------
public static void palindrome() {
String str = "abcdcbaa";
int lengthstr = str.length();
int midLength = Math.abs(lengthstr/2);//////Math.abs
ArrayList<String> alist = new ArrayList<>();
ArrayList<String> blist = new ArrayList<>();
ArrayList<String> clist = new ArrayList<>();
for(int i=0;i<midLength;i++) {
alist.add(Character.toString(str.charAt(i)));
}
for(int j=midLength+1;j<lengthstr;j++) {/////// very imp
blist.add(Character.toString(str.charAt(j)));
}
for(int i=blist.size()-1;i>=0;i--) {
clist.add(blist.get(i));
}
System.out.println(alist);
System.out.println(blist);
System.out.println(clist);
boolean isPalindrome = false;
if(alist.equals(clist)) {//////imp
isPalindrome = true;
}
System.out.println(isPalindrome);
/////////////////////////integer///////////////////////////////
int num = 123454321;
String strr = Integer.toString(num); /////this is main thing, you can not use charAt or num.length with int value
int lengthnum = strr.length();
int midLengthnum = Math.abs(lengthnum/2);//////Math.abs
ArrayList<String> dlist = new ArrayList<>();
ArrayList<String> elist = new ArrayList<>();
ArrayList<String> flist = new ArrayList<>();
for(int i=0;i<midLengthnum;i++) {
dlist.add(Character.toString(strr.charAt(i)));
}
for(int j=midLengthnum+1;j<lengthnum;j++) {/////// very imp
elist.add(Character.toString(strr.charAt(j)));
}
for(int i=elist.size()-1;i>=0;i--) {
flist.add(elist.get(i));
}
System.out.println(dlist);
System.out.println(elist);
System.out.println(flist);
boolean isPalindromeNum = false;
if(dlist.equals(flist)) {
isPalindromeNum = true;
}
System.out.println(isPalindromeNum);
}
//-------------------method 5----------------------------
public static void reformatGivenText() {
String str = "bbbaadddddu"; //output should be "3a-2b-4d-1u"
String[] strArray = new String[str.length()];
int lgth = str.length();
for(int i=0;i<lgth;i++) {
strArray[i]= Character.toString(str.charAt(i));
}
System.out.println("Array = "+Arrays.toString(strArray));//[b, b, b, a, a, d, d, d, d, d, u]
ArrayList<String> alist = new ArrayList<>();//unique chars
ArrayList<Integer> blist = new ArrayList<>();//index of unique chars
ArrayList<Integer> clist = new ArrayList<>();//count of each unique chars
ArrayList<String> dlist = new ArrayList<>();//combined number and char
for(int i=1;i<lgth;i++) {
if(!(strArray[i]).equals(strArray[i-1])) {
alist.add(strArray[i-1]);
blist.add(i-1);
}
}
alist.add(strArray[lgth-1]);
blist.add(lgth-1);
System.out.println("alist = "+alist);//[b, a, d, u]
System.out.println("blist = "+blist);//[2, 4, 9, 10]
clist.add(blist.get(0)+1);
for(int i=1;i<blist.size();i++) {
clist.add(blist.get(i)-blist.get(i-1));
}
System.out.println("clist = "+clist);//[2, 4, 9, 10]
for(int i=0;i<blist.size();i++) {
dlist.add( Integer.toString(clist.get(i)).concat(alist.get(i)));
}
System.out.println("dlist = "+dlist);//[3b, 2a, 5d, 1u]
String result = dlist.get(0);
for(int i=1;i<blist.size();i++) {
//result = result+"-"+dlist.get(i); //OR
result = result.concat("-").concat(dlist.get(i));
}
System.out.println("result = "+result);//3b-2a-5d-1u
}
//-------------------method 6----------------------------
public static void sumValueOfaString() {
String str ="Hello WorldaA";
int asciiValueofa = 'a';
int asciiValueofA = 'A';
int asciiValueofz = 'z';
int asciiValueofZ = 'Z';
System.out.println("samll letters a-z:"+asciiValueofa+"-"+asciiValueofz);//97-122
System.out.println("Cap letters A-Z:"+asciiValueofA+"-"+asciiValueofZ);//65-90
int sumValue = 0;
for(int i=0;i<str.length();i++) {
int x = str.charAt(i);
System.out.println("x= "+x);
sumValue=sumValue+x;
}
System.out.println(sumValue);
}
public static void removeDuplicateChars1() {
String str = "this is a beautiful world.";
String[] strArray = new String[str.length()];
for(int i=0;i<str.length();i++) {
strArray[i]= Character.toString(str.charAt(i));
}
System.out.println("Array1 = "+Arrays.toString(strArray));//[t, h, i, s, , i, s, , a, , b, e, a, u, t, i, f, u, l, , w, o, r, l, d, .]
Arrays.sort(strArray);
System.out.println("Array1 = "+Arrays.toString(strArray));//[ , , , , ., a, a, b, d, e, f, h, i, i, i, l, l, o, r, s, s, t, t, u, u, w]
ArrayList<String> alist = new ArrayList<>();
for(int i=1;i<str.length();i++) {
if(!(strArray[i-1].equals(strArray[i]))) {
alist.add(strArray[i]);
}
}
alist.add(strArray[strArray.length-1]);
System.out.println("unique chars = "+alist);//[., a, b, d, e, f, h, i, l, o, r, s, t, u, w, w]
}
public static void removeAllArrayList() { //subtract/remove array elements using another array using removeAll keyword.
ArrayList<Integer> alist = new ArrayList<>();
ArrayList<Integer> blist = new ArrayList<>();
ArrayList<Integer> clist = new ArrayList<>();
for(int i=0;i<5;i++) {
alist.add(i);
}
System.out.println(alist);
blist = alist;
System.out.println(blist);
blist.remove(4) ;
System.out.println(blist);
alist.removeAll(blist);
System.out.println(alist);
}
//-------------------method 7----------------------------
public static void sumTestfromArray() {
int[] intArray = {1,3,4,5,7,8,9,2};
for(int i=0;i<intArray.length; i++) {
for(int j=0;j<intArray.length; j++) {
if((!(i==j)) && ((intArray[i]+intArray[j])==10)) {
//if((intArray[i]+intArray[j])==10) {
System.out.println(intArray[i]+"-------------"+intArray[j]);
System.out.println("-------------");
//}
}
}
}
}
//-------------------method 9----------------------------
public static void startingAndEndgingDigitSame() {
int num = 12221;
String str = Integer.toString(num);
int len = str.length();
if((Character.toString(str.charAt(0))).equals(Character.toString(str.charAt(len-1)))) {
System.out.println("Same");
} else {
System.out.println("NOT Same");
}
}
//-------------------method 10----------------------------
public static void countUpperlower() {
String str = "HelloHello";
System.out.println(str.toUpperCase());
System.out.println(str.toLowerCase());
int upCount = 0;
int lowCount = 0;
for(int i=0; i<str.length();i++) {
String UpperStr = Character.toString(str.charAt(i)).toUpperCase();
if(((Character.toString(str.charAt(i))).equals(UpperStr))){
upCount ++;
} else {
lowCount++;
}
}
System.out.println(upCount);
System.out.println(lowCount);
}
//-------------------method 11----------------------------
public static String caseTest(int month) {
String convertedMonth ;
switch(month){
case 1 : convertedMonth = "1st";
break ;
case 2 : convertedMonth = "2nd";
break ;
default : convertedMonth = "enter valid month";
break ;
}
return convertedMonth ;
}
}