【2019.07.04】java 数组选择排序，二分法查找

数组选择排序

• 选择数列中的最小数，然后将它和数列中的第一个数字互换

/**
	 * 数组选择排序
	 * @param list 待排序的数组
	 * @return
	 */
	private static double[] selectionSort(double[] list) {
		for (int i = 0; i < list.length; i++) {
			double currentMin = list[i];
			int currentMinIndex = i;
		
			for (int j = i + 1; j < list.length; j++) {
				if (currentMin > list[j]) {
					currentMin = list[j];
					currentMinIndex = j;
				}
			}
			
			if (currentMinIndex != i) {
				list[currentMinIndex] = list[i];
				list[i] = currentMin;
			}
		}
		return list;
	}

数组二分法查找

• 前提：数组中的元素必须已经按照从大到小或从小到大排序好

/**
	 * 二分查找
	 * @param list 数组
	 * @param key 待查找元素
	 * @return 待查找元素的下标/-1
	 */
	private static int binarySearch(double[] list, double key) {
		int low = 0;
		int high = list.length -1;
		
		while (high >= low) {
			int mid = (low + high) / 2;
			if (key < list[mid])
				high = mid - 1;
			else if(key == list[mid])
				return mid;
			else
				low = mid + 1;
		}
		
		return -1;
	}

测试类

package com.ybs.practice;

import javax.sound.midi.MidiChannel;

/**
* @Description 类描述：数组选择排序
* @ClassName 类名称：
* @author yb.w
* @version 创建时间：2019年7月4日 下午5:23:33
*/
public class SelectionSort {
	public static void main(String[] args) {
		
		double[] list = {1, -3, 9 , 4.5, 6.6, 5.7, -4.5};
		double[] result = selectionSort(list);
		
		int binarySearch = binarySearch(result, 6.6);
		System.out.println(binarySearch);
	}
	
	/**
	 * 数组选择排序
	 * @param list 待排序的数组
	 * @return
	 */
	private static double[] selectionSort(double[] list) {
		for (int i = 0; i < list.length; i++) {
			double currentMin = list[i];
			int currentMinIndex = i;
		
			for (int j = i + 1; j < list.length; j++) {
				if (currentMin > list[j]) {
					currentMin = list[j];
					currentMinIndex = j;
				}
			}
			
			if (currentMinIndex != i) {
				list[currentMinIndex] = list[i];
				list[i] = currentMin;
			}
		}
		return list;
	}
	
	/**
	 * 二分查找
	 * @param list 数组
	 * @param key 待查找元素
	 * @return 待查找元素的下标/-1
	 */
	private static int binarySearch(double[] list, double key) {
		int low = 0;
		int high = list.length -1;
		
		while (high >= low) {
			int mid = (low + high) / 2;
			if (key < list[mid])
				high = mid - 1;
			else if(key == list[mid])
				return mid;
			else
				low = mid + 1;
		}
		
		return -1;
	}
}