二分查找(oc/java/Python/scala)

查找過程演示：

在數組[130,150,170,190,210,230,250,270,290,310]中查找數字190，紅色爲二分線(折半線)，灰色爲查找區域，黑色爲排除區域。

SYJ二分查找演示.gif

二分查找優缺點：

二分查找(折半查找)優勢是比較次數少，查找速度快，平均性能好；其缺點是要求待查表爲有序表，且插入刪除困難。時間複雜度能夠表示O(h)=O(log2n)，以2爲底，n的對數。好比數組長度爲10，最多找4次。

objectIve-c實現代碼：

#import <Foundation/Foundation.h>

int search(NSArray *array,int item){
    int x = 1;
    int low = 0;
    int high = (int)[array count] - 1;
    while (low <= high) {
        NSLog(@"第%d次比較",x);
        x++;
        int mid = (high+low)/2;
        if(item == [array[mid] intValue]){
            NSLog(@"%d找到了,在第%d個位置",item,mid);
            return mid;
        }else if(item < [array[mid] intValue]){
            NSLog(@"%d比%d大，繼續查找",[array[mid] intValue],item);
            high = mid-1;
        }else{
            NSLog(@"%d比%d小，繼續查找",[array[mid] intValue],item);
            low = mid+1;
        }
    }
    return -1;
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSLog(@"請輸入要查詢的數字:");
        int x;
        scanf("%d",&x);
        NSArray *array = @[@1,@3,@5,@7,@9,@11,@13,@15,@17,@19,@21,@23,@25];
        int jieguo = search(array,x);
        if(jieguo == -1){
            NSLog(@"沒找到要查找的數字");
        }
    }
    return 0;
}複製代碼

運行截圖：

1.png

java實現代碼：

import java.util.Scanner;
public class PaiXu{
    public static void main(String[] args){
        Integer[] haha = {1,3,5,7,9,11,13,15,17,19,21,23,25,27};
        Scanner sc = new Scanner(System.in);
        System.out.println("請輸入您要查找的值：");
        int z = sc.nextInt();
        int y = binarySearch(haha,z);
        if(y == -1){
            System.out.println("要查找的值不存在");
        }
    }

    public static int binarySearch(Integer[] srcArray,int des){
        int x = 1;
        int low = 0;
        int high = srcArray.length-1;
        while(low<=high){
            System.out.println("第"+x+"次比較");
            x++;
            int mid = (high+low)/2;
            if(des == srcArray[mid]){
                System.out.println(des+"找到了,在第"+mid+"個位置");
                return mid;
            }else if(des < srcArray[mid]){
                System.out.println(srcArray[mid]+"比"+des+"大，繼續查找");
                high = mid-1;
            }else{
                System.out.println(srcArray[mid]+"比"+des+"小，繼續查找");
                low = mid+1;
            }
        }
        return -1;
    }
}複製代碼

運行截圖：

2.png

Python實現代碼：

def binary_search(list,item):
    x = 1
    low = 0
    high = len(list)-1
    while low <= high:
        print('第%d次比較'%x)
        x=x+1
        mid = (low+high)//2
        guess = list[mid]
        if guess == item:
            print('找到了,在第%d個位置'%mid)
            return mid
        if guess > item:
            print('%d比%d大，繼續查找'%(guess,item))
            high = mid-1
        else:
            print('%d比%d小，繼續查找'%(guess,item))
            low = mid+1
    print('找不到%d'%item)
    return None
my_list = [1,3,5,7,9,11,13,15,17,19,21,23,25]
z = int(input('請輸入要查找的數字:'))
binary_search(my_list,z)複製代碼

運行截圖：

scala實現代碼：

object ErFen{
    def main(args:Array[String]){
        //var z:Array[Int] = new Array[Int](14);
        //var z = new Array[Int](14);
        var z = Array(1,3,5,7,9,11,13,15,17,19,21,23,25,27);
        var y:Int = search(z,15);
        if(y == -1){
            println("要查找的值不存在");
        }
    }

    def search(arr:Array[Int],des:Int):Int={
        var x:Int = 1;
        var low:Int = 0;
        var high:Int = arr.length-1;
        while(low <= high){
            println("第"+x+"次比較");
            x += 1;
            var mid:Int = (high+low)/2;
            if(des == arr(mid)){
                println(des+"找到了，在第"+mid+"個位置");
                return mid;
            }else if(des < arr(mid)){
                println(arr(mid)+"比"+des+"大，繼續查找");
                high = mid - 1;
            }else{
                println(arr(mid)+"比"+des+"小，繼續查找");
                low = mid + 1;
            }
        }
        return -1;
    }
}複製代碼

運行截圖：

Snip20170602_4.png