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  • 二分查找问题(Java版)

    二分查找问题(Java版)
     
    1.一般实现
    package search;
     
    /**
     * @author lei 2011-8-17
     */
    public class BinarySearch {
        /**
         * 二分查找
         *
         * 注意：二分查找只是针对有序排列的各种数组或集合
         *
         * @param target
         * @param array
         * @return
         */
        static boolean binarySearch(int target, int[] array) {
            int front = 0;
            int tail = array.length - 1;
            // 判断子数组是否能再次二分
            while (front <= tail) {
                // 获取子数组的中间位置，并依据此中间位置进行二分
                int middle = (front + tail) / 2;
     
                if (array[middle] == target) {
                    return true;
                } else if (array[middle] > target) {
                    tail = middle - 1;
                } else {
                    front = middle + 1;
                }
            }
            return false;
        }
     
        public static void main(String[] args) {
            int[] array = new int[] { 1, 2, 3, 5, 7, 9, 17, 121, 4545 };
            System.out.println(binarySearch(4545, array));
        }
    }
     
     
     
     

    2.Java实现折半查找(二分查找)的递归和非递归算法

     
    1. Java二分查找实现,欢迎大家提出交流意见.  
    2. /** 
    3. *名称:BinarySearch 
    4. *功能:实现了折半查找(二分查找)的递归和非递归算法. 
    5. *说明: 
    6. *     1、要求所查找的数组已有序,并且其中元素已实现Comparable<T>接口,如Integer、String等. 
    7. *    2、非递归查找使用search();,递归查找使用searchRecursively(); 
    8. * 
    9. *本程序仅供编程学习参考 
    10. * 
    11. *@author:   Winty 
    12. *@date:     2008-8-11 
    13. *@email:    wintys@gmail.com 
    14. */  
    15.   
    16. class BinarySearch<T extends Comparable<T>> {  
    17.     private T[]  data;//要排序的数据  
    18.   
    19.     public BinarySearch(T[] data){  
    20.         this.data = data;  
    21.     }  
    22.   
    23.     public int search(T key){  
    24.         int low;  
    25.         int high;  
    26.         int mid;  
    27.   
    28.         if(data == null)  
    29.             return -1;  
    30.   
    31.         low = 0;  
    32.         high = data.length - 1;  
    33.   
    34.         while(low <= high){  
    35.             mid = (low + high) / 2;  
    36.             System.out.println("mid " + mid + " mid value:" + data[mid]);///  
    37.               
    38.             if(key.compareTo(data[mid]) < 0){  
    39.                 high = mid - 1;  
    40.             }else if(key.compareTo(data[mid]) > 0){  
    41.                 low = mid + 1;  
    42.             }else if(key.compareTo(data[mid]) == 0){  
    43.                 return mid;  
    44.             }  
    45.         }  
    46.   
    47.         return -1;  
    48.     }  
    49.   
    50.     private int doSearchRecursively(int low , int high , T key){  
    51.         int mid;  
    52.         int result;  
    53.   
    54.         if(low <= high){  
    55.             mid = (low + high) / 2;  
    56.             result = key.compareTo(data[mid]);  
    57.             System.out.println("mid " + mid + " mid value:" + data[mid]);///  
    58.               
    59.             if(result < 0){  
    60.                 return doSearchRecursively(low , mid - 1 , key);  
    61.             }else if(result > 0){  
    62.                 return doSearchRecursively(mid + 1 , high , key);  
    63.             }else if(result == 0){  
    64.                 return mid;  
    65.             }  
    66.         }  
    67.           
    68.         return -1;  
    69.     }  
    70.   
    71.     public int searchRecursively(T key){  
    72.         if(data ==null)return -1;  
    73.   
    74.         return doSearchRecursively(0 , data.length - 1 , key);  
    75.     }  
    76.   
    77.     public static void main(String[] args){  
    78.         Integer[] data = {1 ,4 ,5 ,8 ,15 ,33 ,48 ,77 ,96};  
    79.         BinarySearch<Integer> binSearch = new BinarySearch<Integer>(data);  
    80.         //System.out.println("Key index:" + binSearch.search(33) );  
    81.   
    82.         System.out.println("Key index:" + binSearch.searchRecursively(3) );  
    83.   
    84.         //String [] dataStr = {"A" ,"C" ,"F" ,"J" ,"L" ,"N" ,"T"};  
    85.         //BinarySearch<String> binSearch = new BinarySearch<String>(dataStr);  
    86.         //System.out.println("Key index:" + binSearch.search("A") );  
    87.     }  
    88. }  
     
     
     
     
     
     
     
     
     
     

    3.二分查找法实现有序数组元素的查找

    package OrderedArray;
     
    /**
     * 有序数组
     * @author anan
     */
    import java.util.Scanner;
     
    class OrderedArray {
        private int[] array;
        private int nElems;
     
        // 构造函数，生成有序数组对象
        public OrderedArray(int max) {
            // 生成数组对象
            array = new int[max];
            // 数组初始元素值为0
            nElems = 0;
        }
     
        // 返回数组大小
        public int size() {
            return nElems;
        }
     
        // 二分查找
        public int BinarySearch(int searchKey) {
            int lowBound = 0;
            int highBound = nElems - 1;
            int currentIndex;
            while (true) {
                currentIndex = (lowBound + highBound) / 2;
                if (array[currentIndex] == searchKey)
                    // 返回数组中key所在位置
                    return currentIndex;
                if (lowBound > highBound)
                    return nElems;
                else {
                    if (array[currentIndex] < searchKey) {
                        lowBound = currentIndex + 1;
                    } else if (array[currentIndex] > searchKey) {
                        highBound = currentIndex - 1;
                    }
                }
            }
        }
     
        // 输入要查找的数
        public int input() {
            Scanner sc = null;
            System.out.println("please input the key you want to search --->");
            sc = new Scanner(System.in);
            int searchKey = sc.nextInt();
            sc.close();
            return searchKey;
        }
     
        // 显示数组元素
        public void display() {
            for (int i = 0; i < nElems; i++) {
                System.out.print(array[i] + " ");
            }
        }
     
        // 插入操作
        public void insert(int value) {
            int i;
            for (i = 0; i < nElems; i++) {
                if (array[i] > value) {
                    break;
                }
            }
            for (int j = nElems; j > i; j--) {
                // 数组元素依次向后移动一位
                array[j] = array[j - 1];
            }
     
            array[i] = value;
            nElems++;
        }
     
        // 删除操作
        public boolean delete(int value) {
            boolean flag = false;
            int j = BinarySearch(value);
            if (j == nElems)
                flag = false;
            else {
                for (int k = j; k < nElems; k++) {
                    array[k] = array[k + 1];
                }
                nElems--;
                flag = true;
            }
            return flag;
        }
     
    };
     
    public class OrderedArrayDemo {
     
        public static void main(String[] args) {
            int maxSize = 100;
            OrderedArray arr = new OrderedArray(maxSize);
            arr.insert(11);
            arr.insert(32);
            arr.insert(5);
            arr.insert(26);
            arr.insert(45);
            arr.insert(88);
            arr.insert(1);
            arr.insert(9);
            arr.delete(9);
            arr.delete(88);
            System.out.println(arr.size());
            System.out.println("---------------------");
            arr.display();
            System.out.println();
            int key = arr.input();
            if (arr.BinarySearch(key) != arr.size()) {
                System.out.println("found the key!");
            } else {
                System.out.println("not found the key!");
            }
     
        }
    }
     
     
     
     
     
     

    4.二分查找示例二（对链表进行查找）

    成员类：
    package com.junglesong; public class Member implements Comparable{     private String name;     private int age;          public Member(String name,int age){         this.name=name;         this.age=age;     }          /**      * 实现成员比较      */     public int compareTo(Object obj){         Member another=(Member)obj;         return this.name.compareTo(another.name);     }          /**      * 实现成员相等运算      */     public boolean equals(Object obj){         Member another=(Member)obj;         return this.name.equals(another.name);     }          public String toString(){         return "名="+name+" 年龄="+age;     }     public int getAge() {         return age;     }     public void setAge(int age) {         this.age = age;     }     public String getName() {         return name;     }     public void setName(String name) {         this.name = name;     } }


    二分查找类：
    package com.junglesong; import java.util.ArrayList; import java.util.List; /**  * 二分查找示例二（对链表进行查找）  * @author: sitinspring(junglesong@gmail.com)  * @date: 2008-3-8  */ public class BinSearch2{     public static void main(String[] args){         // 欲查找的链表         List<Member> members=new ArrayList<Member>();         members.add(new Member("Andy",21));         members.add(new Member("Bill",22));         members.add(new Member("Cindy",23));         members.add(new Member("Douglas",24));         members.add(new Member("Felex",25));         members.add(new Member("Green",26));                  // 测试链表         List<Member> tempList=new ArrayList<Member>();         tempList.add(new Member("Bill",22));         tempList.add(new Member("Cindy",23));         tempList.add(new Member("Douglas",24));         tempList.add(new Member("Felex",25));         tempList.add(new Member("Hill",26));                  for(Member member:tempList){             System.out.println("成员"+member+"的下标为"+binSearch(members,member));         }     }          /**      * 二分查找      * @param sortedArray 已排序的欲查找的链表      * @param seachValue 查找的值      * @return 找到的元素下标，若找不到则返回-1      */     public static int binSearch(List<Member> sortedList,Member seachValue){         // 左边界         int leftBound=0;         // 右边界         int rightBound=sortedList.size()-1;         // 当前下标位置         int curr;                  while(true){             // 定位在左边界和右边界中间             curr=(leftBound+rightBound)/2;                          if(sortedList.get(curr).equals(seachValue)){                 // 找到值                 return curr;             }             else if(leftBound>rightBound){                 // 左边界大于右边界，已经找不到值                 return -1;             }             else{                 if(sortedList.get(curr).compareTo(seachValue)<0){                     // 当当前下标对应的值小于查找的值时，缩短左边界                     leftBound=curr+1;                 }                 else{                     // 当当前下标对应的值大于查找的值时，缩短右边界                     rightBound=curr-1;                 }             }         }     } }
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  • 原文地址：https://www.cnblogs.com/think90/p/6379745.html
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