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Does a “binary sort” algorithm exist?

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孤独总比滥情好
孤独总比滥情好 2021-01-07 21:59

Is there a sorting algorithm that is named \"binary sort\"? Like merge sort, selection sort, or the other kinds of sorting, does a binary sort exist?

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  • 醉酒成梦
    醉酒成梦 (楼主)
    2021-01-07 22:56

    The JDK uses a "binary sort" for arrays < size 32 within its Arrays.sort() method. This is actually an insertion sort but using binary search to find the next item instead of linear search.

    Here is the code from JDK7

    private static void binarySort(Object[] a, int lo, int hi, int start) {
    assert lo <= start && start <= hi;
    if (start == lo)
        start++;
    for ( ; start < hi; start++) {
        @SuppressWarnings("unchecked")
        Comparable pivot = (Comparable) a[start];

        // Set left (and right) to the index where a[start] (pivot) belongs
        int left = lo;
        int right = start;
        assert left <= right;
        /*
         * Invariants:
         *   pivot >= all in [lo, left).
         *   pivot <  all in [right, start).
         */
        while (left < right) {
            int mid = (left + right) >>> 1;
            if (pivot.compareTo(a[mid]) < 0)
                right = mid;
            else
                left = mid + 1;
        }
        assert left == right;

        /*
         * The invariants still hold: pivot >= all in [lo, left) and
         * pivot < all in [left, start), so pivot belongs at left.  Note
         * that if there are elements equal to pivot, left points to the
         * first slot after them -- that's why this sort is stable.
         * Slide elements over to make room for pivot.
         */
        int n = start - left;  // The number of elements to move
        // Switch is just an optimization for arraycopy in default case
        switch (n) {
            case 2:  a[left + 2] = a[left + 1];
            case 1:  a[left + 1] = a[left];
                     break;
            default: System.arraycopy(a, left, a, left + 1, n);
        }
        a[left] = pivot;
    }
}

    
    
             
    
                                                        
    
            
            
    
              
                
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