这个“ mergeSort”有什么问题？

Question

There's a mergeSort code that I copied at class lesson, can you help me to find the errors?

When I run the main that use mergeSort the program enters in an infinite loop but doesn't display any error. I tried to run in debug mode but I am not very expert and I don't find what's wrong. However I think that the error is in mergeSort(int[] v, int inf, int sup) recursion.

public class CopyOfSortMethods {

private static void merge(int[] v, int inf, int med, int sup) {
    int aux[] = new int[v.length];
    int i = inf;
    int j = med + 1;
    int k = inf;

    while ((i <= med) && (j <= sup)) {
        if (v[i] < v[j]) {
            aux[k] = v[i];
            i++;
            k++;
        } else {
            aux[k] = v[j];
            j++;
            k++;
        }
    }
    while (i <= med) {
        aux[k] = v[i];
        i++;
        k++;
    }
    while (j <= sup) {
        aux[k] = v[j];
        j++;
        k++;
    }
    for (i = 0; i <= sup; i++) {
        v[i] = aux[i];
    }
}

public static void mergeSort(int[] v, int inf, int sup) {
    int med;

    while (inf < sup){
        med = (inf + sup)/2;
        mergeSort(v, inf, med);
        mergeSort(v, med + 1, sup);
        merge(v, inf, med, sup);
    }
}

public static void mergeSort(int[] v) {
    if(v!=null) {
        mergeSort(v, 0, v.length - 1);
    }

}
}

Answer 1

As Maverik points out, the issue is the while loop in mergeSort() .

inf and sup are never modified, so inf is always less than sup . The loop never terminates.

Answer 2

The problems in your merge sort (based in the comments):

1. In mergeSort method, you're recursively calling the mergeSort inside a while loop and never changing the values of inf and sup . Change this for an if instead.

     if (inf < sup) { //code goes here... } 

2. In your merge sort, at the bottom of the method body, you're moving the items all the items from aux array to v array. You should only move the elements between inf and sup :

    //for (i = 0; i <= sup; i++) { for (i = inf; i <= sup; i++) { //code goes here... }