Writing an algorithm for insertion sort in java

Question

I'm trying to implement insertion sort in Java. I think something isn't quite right with my code.

public int[] sort(int[] unsorted) {
    int i, j, v;
    for (i = 1; i < unsorted.length - 1; i++) {
        v = unsorted[i];
        j = i;

        while (unsorted[j-1] > v && j >= 1) {
            unsorted[j] = unsorted[j -1];
            j--;
        }
        unsorted[j] = v;
    }
    return unsorted;
}

I get an IndexOutOfBoundsException for my while loop ([j-1]). But how can I rewrite the code so it actually works?

HINT: What happens in your while statement condition when j has just been decremented down to zero? You need to check first if the value of j is "safe" before accessing unsorted[j-1]. — Kevin Anderson
– Kevin Anderson, Commented Mar 1, 2021 at 13:58
as a suggestion, do not call it unsorted. Returning unsorted from a method called sort is misleading, at least. Just source, or similar. — aran
– aran, Commented Mar 2, 2021 at 0:57

aran · Accepted Answer · 2021-03-02 00:54:41Z

2

For index i, you can simply start the index j from i-1. And in the while loop, always put the index validity check first, before accessing data from that index. The following code solves your problem:

public int[] sort(int[] unsorted) {
    int i, j, v;
    for (i = 1; i < unsorted.length; i++) {
        v = unsorted[i];
        j = i - 1;

        while (j >= 0 && unsorted[j] > v) {
            unsorted[j + 1] = unsorted[j];
            j--;
        }
        unsorted[j + 1] = v;
    }
    return unsorted;
}

edited Mar 2, 2021 at 0:54

aran

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answered Mar 1, 2021 at 15:08

biqarboy

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3 Comments

aran Over a year ago

it does, no doubts ; )

biqarboy Over a year ago

I agree with you! :) Old habit to say like this.

aran Over a year ago

I do it, too. But better to show security. You solved it, 100%.

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