Ejemplo n.º 1
0
        /// <summary>
        ///  Rearranges the array so that a[k]} contains the kth smallest key;
        ///  a[0] through a[k-1] are less than (or equal to) a[k];
        ///  a[k+1] through a[n-1] are greater than (or equal to) a[k].
        /// </summary>
        /// <param name="a">the array</param>
        /// <param name="k">the rank of the key</param>
        /// <returns>the key of rank k}</returns>
        public static T Select(T[] a, int k)
        {
            if (k < 0 || k >= a.Length)
            {
                throw new ArgumentOutOfRangeException(nameof(k), k, "out of bounds");
            }
            StdRandom.shuffle(a);

            int lo = 0, hi = a.Length - 1;

            while (hi > lo)
            {
                int i = partition(a, lo, hi);
                if (i > k)
                {
                    hi = i - 1;
                }
                else if (i < k)
                {
                    lo = i + 1;
                }
                else
                {
                    return(a[i]);
                }
            }
            return(a[lo]);
        }
Ejemplo n.º 2
0
        /// <summary>
        /// Randomized insertion.
        /// make new node the root with uniform probability
        /// </summary>
        /// <param name="x"></param>
        /// <param name="key"></param>
        /// <param name="val"></param>
        /// <returns></returns>
        internal override BaseNode <TKey, TValue> PutKey(BaseNode <TKey, TValue> x, TKey key, TValue val)
        {
            if (x == null)
            {
                return(new BaseNode <TKey, TValue>(key, val, 1));
            }
            int cmp = key.CompareTo(x.key);

            if (cmp == 0)
            {
                x.val = val;
                return(x);
            }

            if (StdRandom.bernoulli(1.0 / (x.Size + 1.0)))
            {
                return(PutRoot(x, key, val));
            }
            if (cmp < 0)
            {
                x.left = PutKey(x.left, key, val);
            }
            else
            {
                x.right = PutKey(x.right, key, val);
            }

            x.UpdateSize();
            return(x);
        }
Ejemplo n.º 3
0
        /// <summary>
        /// Rearranges the array in ascending order, using the natural order.
        /// </summary>
        /// <param name="a">the array to be sorted</param>
        public static void Sort(T[] a)
        {
            StdRandom.shuffle(a);

            sort(a, 0, a.Length - 1);
            Debug.Assert(SortingHelper <T> .isSorted(a));
        }
Ejemplo n.º 4
0
        /// <summary>
        /// Randomized deletion.
        /// </summary>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <returns></returns>
        private BaseNode <TKey, TValue> joinLR(BaseNode <TKey, TValue> a, BaseNode <TKey, TValue> b)
        {
            if (a == null)
            {
                return(b);
            }
            if (b == null)
            {
                return(a);
            }

            if (StdRandom.bernoulli((double)a.Size / (a.Size + b.Size)))
            {
                a.right = joinLR(a.right, b);
                a.UpdateSize();
                return(a);
            }
            else
            {
                b.left = joinLR(a, b.left);
                b.UpdateSize();
                return(b);
            }
        }