二分查找

// 非递归写法public static int search(int[] arr,int des){    int left = 0;    int right = arr.length - 1;//arr长度-1    while(left<=right){        int mid = (left+right)/2;        if(des == arr[mid]){            return 1;//相等返回1        }else if(des < arr[mid]){//目标小于中间值，变换右值            right = mid -1;        }else{            left = mid + 1;        }    }    return -1;}// 递归写法public static int search(int[] arr,int left,int right,int key){    if(left <= right){        int mid = (left+right)/2;        if(key == arr[mid]){            return mid;        }else if(key<arr[mid]){            return search(arr,left,mid-1,key);        }else{            return search(arr,mid+1,right,key);        }    }else{        return -1;    }}