I am new to Java and have tried to implement mergesort in Java. However, even after running the program several times, instead of the desired sorted output, I am getting the same user given input as the output. I would be thankful if someone could help me understand this unexpected behaviour.
import java.io.*;
import java.util.Arrays;
public class MergeSort {
public static void main(String[] args) throws IOException {
BufferedReader R = new BufferedReader(new InputStreamReader(System.in));
int arraySize = Integer.parseInt(R.readLine());
int[] inputArray = new int[arraySize];
for (int i = 0; i < arraySize; i++) {
inputArray[i] = Integer.parseInt(R.readLine());
}
mergeSort(inputArray);
for (int j = 0; j < inputArray.length; j++) {
System.out.println(inputArray[j]);
}
}
static void mergeSort(int[] A) {
if (A.length > 1) {
int q = A.length / 2;
int[] leftArray = Arrays.copyOfRange(A, 0, q);
int[] rightArray = Arrays.copyOfRange(A, q + 1, A.length);
mergeSort(leftArray);
mergeSort(rightArray);
A = merge(leftArray, rightArray);
}
}
static int[] merge(int[] l, int[] r) {
int totElem = l.length + r.length;
int[] a = new int[totElem];
int i, li, ri;
i = li = ri = 0;
while (i < totElem) {
if ((li < l.length) && (ri < r.length)) {
if (l[li] < r[ri]) {
a[i] = l[li];
i++;
li++;
} else {
a[i] = r[ri];
i++;
ri++;
}
} else {
if (li >= l.length) {
while (ri < r.length) {
a[i] = r[ri];
i++;
ri++;
}
}
if (ri >= r.length) {
while (li < l.length) {
a[i] = l[li];
li++;
i++;
}
}
}
}
return a;
}
}
Here is a corrected version of your code:
import java.io.*;
import java.util.Arrays;
public class MergeSort {
public static void main(String[] args) throws IOException{
BufferedReader R = new BufferedReader(new InputStreamReader(System.in));
int arraySize = Integer.parseInt(R.readLine());
int[] inputArray = new int[arraySize];
for (int i = 0; i < arraySize; i++) {
inputArray[i] = Integer.parseInt(R.readLine());
}
mergeSort(inputArray);
for (int j = 0; j < inputArray.length; j++) {
System.out.println(inputArray[j]);
}
}
static void mergeSort(int[] A) {
if (A.length > 1) {
int q = A.length/2;
//changed range of leftArray from 0-to-q to 0-to-(q-1)
int[] leftArray = Arrays.copyOfRange(A, 0, q-1);
//changed range of rightArray from q-to-A.length to q-to-(A.length-1)
int[] rightArray = Arrays.copyOfRange(A,q,A.length-1);
mergeSort(leftArray);
mergeSort(rightArray);
merge(A,leftArray,rightArray);
}
}
static void merge(int[] a, int[] l, int[] r) {
int totElem = l.length + r.length;
//int[] a = new int[totElem];
int i,li,ri;
i = li = ri = 0;
while ( i < totElem) {
if ((li < l.length) && (ri<r.length)) {
if (l[li] < r[ri]) {
a[i] = l[li];
i++;
li++;
}
else {
a[i] = r[ri];
i++;
ri++;
}
}
else {
if (li >= l.length) {
while (ri < r.length) {
a[i] = r[ri];
i++;
ri++;
}
}
if (ri >= r.length) {
while (li < l.length) {
a[i] = l[li];
li++;
i++;
}
}
}
}
//return a;
}
}