80 lines
2.4 KiB
Java
80 lines
2.4 KiB
Java
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/*************************************************************************
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* Compilation: javac StaticSetOfInts.java
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*
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* Data type to store a set of integers.
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*
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*************************************************************************/
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import java.util.Arrays;
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/**
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* The StaticSETofInts class represents a set of integers.
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* It supports searching for a given integer is in the set. It accomplishes
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* this by keeping the set of integers in a sorted array and using
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* binary search to find the given integer.
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*
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* The rank and contains operations take
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* logarithmic time in the worst case.
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*
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* For additional documentation, see Section 1.2</a> of
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* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
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*
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* @author Robert Sedgewick
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* @author Kevin Wayne
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*/
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public class StaticSETofInts {
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private int[] a;
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/**
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* Initializes a set of integers specified by the integer array.
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* @param keys the array of integers
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* @throws IllegalArgumentException if the array contains duplicate integers
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*/
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public StaticSETofInts(int[] keys) {
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// defensive copy
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a = new int[keys.length];
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for (int i = 0; i < keys.length; i++)
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a[i] = keys[i];
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// sort the integers
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Arrays.sort(a);
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// check for duplicates
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for (int i = 1; i < a.length; i++)
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if (a[i] == a[i-1])
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throw new IllegalArgumentException("Argument arrays contains duplicate keys.");
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}
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/**
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* Is the key in this set of integers?
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* @param key the search key
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* @return true if the set of integers contains the key; false otherwise
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*/
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public boolean contains(int key) {
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return rank(key) != -1;
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}
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/**
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* Returns either the index of the search key in the sorted array
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* (if the key is in the set) or -1 (if the key is not in the set).
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* @param key the search key
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* @return the number of keys in this set less than the key (if the key is in the set)
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* or -1 (if the key is not in the set).
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*/
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public int rank(int key) {
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int lo = 0;
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int hi = a.length - 1;
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while (lo <= hi) {
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// Key is in a[lo..hi] or not present.
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int mid = lo + (hi - lo) / 2;
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if (key < a[mid]) hi = mid - 1;
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else if (key > a[mid]) lo = mid + 1;
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else return mid;
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}
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return -1;
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}
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}
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