2014/5/12之二分查找法

package array_Study;
import java.util.Scanner;
//二分查找
public class binarySearch {

public static void main(String[] args) {
int [] num = {2,89,74,13,56,92,27,61,48,21,63,52,75,69};
sortnumber(num);
binarysearch(num);
}


private static void binarysearch(int[] num) {
//定義起始位置
int start =0;
//定義終止位置
int end=num.length;
//定義要查找的數
Scanner scan = new Scanner(System.in);
System.out.println("\n請輸入在這組數組中你想查找的數:");
int searchnum = scan.nextInt();
for(int i=0;i<num.length;i++){
//取中間值下標
int middle = (start+end)/2;
//正好找到
if(num[middle]==searchnum){
System.out.println("\n你所查找的索引爲:"+middle);
break;
}
//如果中間數大於要查找的數,則往左邊找,並且開始查找的索引往左移一位即  middle-1,
else if(num[middle]>searchnum){
end=middle-1;
}
//如果中間數小於中間數,則往右邊找,並且開始查找的索引往右移一位即  middle+1
else if(num[middle]<searchnum){
start=middle+1;
}
}
}


private static void sortnumber(int[] num) {
//外層循環n-1
for(int i=0;i<num.length-1;i++){
//內層循環n-i-1
for(int j=0;j<num.length-i-1;j++){
if(num[j]>num[j+1]){
//交換位置
int temp =num[j];
num[j]=num[j+1];
num[j+1]=temp;
}
}
}

//遍歷輸出
System.out.print("排序後: ");
for(int i:num){
System.out.print(i+" ");
}
}
}