i'm trying to create a bubble sort but I there is something wrong with my code. The output is : 82345679. I would like it to be : 23456789.
package com.company;
public class Main {
public static void main(String[] args) {
// write your code here
int[] tab = {9,8,7,6,5,4,3,2};
int[] result = {9,8,7,6,5,4,3,2};
for (int i = 0; i < result.length; i++ ) {
if (i < result.length - 1 ) {
if (result[i] > result[i+1]) {
result = permute(result, i);
i = 0;
}
}
}
for (int i: result) {
System.out.print(i);
}
}
public static int[] permute (int[] tableau, int index) {
int temp;
temp = tableau[index];
tableau[index] = tableau[index+1];
tableau[index+1] = temp;
return tableau;
}
}
You need two loops.
int swap;
for (int i = 0; i < ( result.length - 1 ); i++) {
for (int j = 0; j < result.length - 1; j++) {
if (result[j] > result[j+1]) {
swap = result[j];
result[j] = result[j+1];
result[j+1] = swap;
}
}
}
You need to have 2 loops in order to compare each number to the whole array..
example of bubble sorting
public static void bubbleSort(int[] numArray) {
int n = numArray.length;
int temp = 0;
for (int i = 0; i < n; i++) {
for (int j = 1; j < (n - i); j++) {
if (numArray[j - 1] > numArray[j]) {
temp = numArray[j - 1];
numArray[j - 1] = numArray[j];
numArray[j] = temp;
}
}
}
}
Refer to this question
Can be done with ONE loop (although it is not the usual way to present the bubble sort):
public static void main (String args[]) {
int[] tab = {9,8,7,6,5,4,3,2};
int i=1; // let's do the bubble sort again
while (i < tab.length) {
// loop invariant : t[0] <= t[1] .... <= t[i-1]
if (tab[i-1] < tab[i]) { // bubble here
swap(tab, i-1, i);
if (i>1) {
i = i-1; // one step to the left....
}
} else {
i = i +1; // one step to the right
}
}
for (int x: tab) {
System.out.print(x);
}
}
static void swap(int[] t, int i, int j) {
int x = t[i];
t[i] = t[j];
t[j] = x;
}
The issue is with the combination of i = 0
and i++
in the for loop. Whenever you go in the i = 0
branch, you end up restarting at 1
because of the i++
. Resulting in always skipping the 8
after the first iteration where the 9
is moved to the end.
So, either restart at -1
, or use a while loop and only increment in an else block. For example:
int i = 0;
while (i < result.length - 1) {
if (result[i] > result[i+1]) {
permute(result, i)
i = 0;
} else {
i++;
}
}
However, I would advise against the one-loop bubble sort, because the algorithm complexity is harder to see (it is still O(n^2)
, but with only one loop it can give the impression that it is O(n)
).
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