Sorting_Searching 读入数字流求rank @CareerCup

最新推荐文章于 2017-12-04 21:47:06 发布

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本文介绍了一种使用二叉搜索树（BST）实现排名查找算法的方法，通过track和getRankOfNumber方法来实时更新和获取数字排名。

用BST实现

package Sorting_Searching;

import CtCILibrary.AssortedMethods;

/**
 * Imagine you are reading in a stream of integers. Periodically, you wish to be
 * able to look up the rank of a number x (the number of values less than or
 * equal to x). Implement the data structures and algorithms to support these
 * operations. That is, implement the method track(int x), which is called
 * when each number is generated, and the methodgetRankOfNumber (int x), which
 * returns the number of values less than or equal to x (not including x
 * itself).
 * 
 * EXAMPLE
Stream (in order of appearance): 5,  1,  4,  4,  5,  9,  7,  13,  3
getRankOfNumber(l) = 0
getRankOfNumber(3) = 1
getRankOfNumber(4) = 3

 * 不断地读入数字流，要求实现track和getRankOfNumber方法。
 * 
 */
public class S11_8 {

	private static RankNode root = null;

	// track就是插入BST的过程
	public static void track(int number) {
		if (root == null) {
			root = new RankNode(number);
		} else {
			root.insert(number);
		}
	}
	
	// 得到rank就是得到有多少个比number小
	public static int getRankOfNumber(int number) {
        return root.getRank(number);
	}

	public static void main(String[] args) {
		int size = 5;
		int[] list = AssortedMethods.randomArray(size, -10, 10);
		for (int i = 0; i < list.length; i++) {
			track(list[i]);
		}

		int[] tracker = new int[size];
		for (int i = 0; i < list.length; i++) {
			int v = list[i];
			int rank1 = root.getRank(list[i]);
			tracker[rank1] = v;
		}

		for (int i = 0; i < tracker.length - 1; i++) {
			if (tracker[i] != 0 && tracker[i + 1] != 0) {
				if (tracker[i] > tracker[i + 1]) {
					System.out.println("ERROR at " + i);
				}
			}
		}

//		System.out.println("Array: " + AssortedMethods.arrayToString(list));
//		System.out.println("Ranks: " + AssortedMethods.arrayToString(tracker));
		for(int i : list){
			System.out.println(i + ": " + getRankOfNumber(i));
		}
	}

	static class RankNode {
		public int left_size = 0;
		public RankNode left;
		public RankNode right;
		public int data = 0;

		public RankNode(int d) {
			data = d;
		}

		public void insert(int d) {
			if (d <= data) {
				if (left != null) {
					left.insert(d);
				} else {
					left = new RankNode(d);
				}
				left_size++;
			} else {
				if (right != null) {
					right.insert(d);
				} else {
					right = new RankNode(d);
				}
			}
		}

		public int getRank(int d) {
			if (d == data) {
				return left_size;
			} else if (d < data) {
				if (left == null) {
					return -1;
				} else {
					return left.getRank(d);
				}
			} else {
				int right_rank = right == null ? -1 : right.getRank(d);
				if (right_rank == -1) {
					return -1;
				} else {
					return left_size + 1 + right_rank;
				}
			}
		}
	}
}