使用二分法查询二维整型数组的值（找到返回其坐标）

private static String find(int[][] arr, int num) {
    int row = 0;  //控制行数
    while (row < arr.length){
        int left = 0;  //行的左下标
        int right = arr[row].length - 1;   //行的右下标
        while (left <= right) {  //每一行进行二分查找
            if(num > arr[row][right]){  //如果查找的数比该行的最后一个数还大，则直接进入下一行的比较
                break;
            }
            //int mid = (left + right) / 2;
            int mid = (right - left + 1) / 2 + left; //防止相加超过数据类型的上界  
            if (arr[row][mid] == num) {
                return "[" + row + "," + mid + "]";
            } else if (arr[row][mid] > num) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }//退出该层while循环说明该层未找到
        ++row;  //层数加一
    }//退出说明未找到
    return "无该整数";
}

int[][] arr = {{1,3,5},{7,9},{15,19,20}};
String index = find(arr,1);
System.out.println(index);
String index1 = find(arr,20);
System.out.println(index1);
String index2 = find(arr,9);
System.out.println(index2);
String index3 = find(arr,0);
System.out.println(index3);