Java二分查找

Java中有自带Arrays 工具类

Arrays.sort(data);

int index = Arrays.binarySearch(data, 3);

 

直接调用函数即可。index即为数组下标值。

 

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public class er{     public static void main(String[] args){         int[] arr = {0,1,2,3,4,5,6,7,8,9};         int a = 9;         //int m = BinSearch(arr,0,arr.length-1,a);         int m = BinSearch(arr,arr.length,a);         System.out.println(m);     }     /*     //递归     static int BinSearch(int Array[],int low,int high,int key)      {          if (low<=high)          {             int mid = (low+high)/2;              if(key == Array[mid])                  return mid;             else if(key<Array[mid])                  //移动low和high                 return BinSearch(Array,low,mid-1,key);             else if(key>Array[mid])                 return BinSearch(Array,mid+1,high,key);         }          return -1;      }     */     /*     //递归     public static int BinSearch(int[] arr,int begin,int end,int a){         if (begin<=end)         {             int mid = (begin+end)/2;             if (arr[mid] == a){             //System.out.println("1");             return mid;             }             else if (arr[mid] < a){                 return BinSearch(arr,mid+1,end,a);                 //System.out.println("2 "+mid+" "+end);             }             else if (arr[mid] > a){                 return BinSearch(arr,begin,mid-1,a);                 //System.out.println("3"+begin+" "+mid);             }         }                   return -1;     }     */       //普通循环     public static int BinSearch(int[] a, int len, int goal)     {         int low = 0;         int high = len -1;         while (low <= high)         {             int middle = (high - low) / 2 + low; // 直接使用(high + low) / 2 可能导致溢出             if (a[middle] == goal)                 return middle;             //在左半边             else if (a[middle] > goal)                 high = middle - 1;             //在右半边             else                 low = middle + 1;         }         //没找到         return -1;     } }