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二分查找

public class BinarySearch{

public static void main(String[] args) {

int[] arr = {1,3,2,5,6,4,7,9,8}; Arrays.sort(arr); // TODO Auto-generated method stub int low = 0; int high = arr.length-1; while(low<=high){ int mid = (low+high)/2; if(arr[mid]==5){ System.out.println("True"); return; }else{ if(arr[mid]<5){ low = mid+1; }else{ high = mid-1; } } }

}

}

递归实现二分查找

public class RecursiveQuery1{

        public static void f(int[] aa,int bottom,int top,int num){

int mid = (bottom+top)/2; if(top>=bottom){ if(aa[mid]==num){//设置递归出口 System.out.println("True"); return; }else{ if(aa[mid]<5){ f(aa,mid+1,top,num);//若当前的aa[mid]小于5那么要到右边区域中去查找 并让bottom = mid+1 }else{ f(aa,bottom,mid-1,num);//若当前的aa[mid]大于5则到左边区域中去查找 并让high = mid-1 } }   } } public static void main(String[] args) { int[] arr = {1,3,2,5,6,4,7,9,8}; Arrays.sort(arr);//在使用二分查找前 需要对数组进行排序 // TODO Auto-generated method stub int low = 0; int high = arr.length-1; f(arr,low,high,5);//查找5是否在这个数组中  }

}

当要查询的数据量特别多时，二分查找比普通的顺序查找的效率要高的多。

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