归并排序算法 iOS

- ( void )mergeSortArray:( NSMutableArray *)array lowIndex:( NSInteger )lowIndex highIndex:( NSInteger )highIndex
{
    if (lowIndex >= highIndex) {
        return ;
    }
    NSInteger midIndex = lowIndex + (highIndex - lowIndex) / 2 ;
    [ self mergeSortArray :array lowIndex :lowIndex highIndex :midIndex];
    [ self mergeSortArray :array lowIndex :midIndex + 1 highIndex :highIndex];
    [ self mergeArray :array lowIndex :lowIndex midIndex :midIndex highIndex :highIndex];
}

- ( void )mergeArray:( NSMutableArray *)array lowIndex:( NSInteger )lowIndex midIndex:( NSInteger )midIndex highIndex:( NSInteger )highIndex
{
    for ( NSInteger i = lowIndex; i <= highIndex; i ++) {
        self . tempArr [i] = array[i];
    }
   
    NSInteger k = lowIndex;
    NSInteger l = midIndex + 1 ;
    for ( NSInteger j = lowIndex; j <= highIndex; j ++) {
        if (l > highIndex) {
            array[j] = self . tempArr [k];
            k++;
        } else if (k > midIndex)
        {
            array[j] = self . tempArr [l];
            l++;
        } else if ([ self . tempArr [k] integerValue ] > [ self . tempArr [l] integerValue ])
        {
            array[j] = self . tempArr [l];
            l++;
        } else
        {
            array[j] = self . tempArr [k];
            k++;
        }
    }

}