JAVA语言程序设计基础篇（Chapter 8）课后习题参考答案

1. (简答题)(Locate the largest element) Write the following method that returns the location  of the largest element in a two-dimensional array. 

    public static int[] locateLargest(double[][] a)   

The return value is a one-dimensional array that contains two elements. These  two elements indicate the row and column indices of the largest element in the  two-dimensional array. Write a test program that prompts the user to enter a two-dimensional array and displays the location of the largest element in the array.  Here is a sample run:

    Enter the number of rows and columns of the array: 3 4 

    Enter the array:  

    23.5  35  2     10

    4.5    3   45    3.5 

    35    44  5.5   9.6 The location of the largest element is at (1, 2)

import java.util.Scanner;

public class Demo18 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number of rows and columns of the array :");
        int row = sc.nextInt();
        int column=sc.nextInt();
        double [][] array = new double[row][column];
        System.out.println("Enter the array :");
        for (int i = 0; i < row; i++) {
            for (int i1 = 0; i1 < column; i1++) {
                array[i][i1]=sc.nextDouble();
            }
        }
        int[] location = locateLargest(array);
        System.out.println("The location of the largest elements is at ("+location[0]+","+location[1]+")");
    }
    public static int[] locateLargest(double[][] a){
        int [] location = {0,0};

        for (int i = 0; i < a.length; i++) {
            for (int j = 0; j < a[0].length; j++) {
                if(a[location[0]][location[1]]<a[i][j]){
                    location[0]=i;
                    location[1]=j;
                }
            }
        }
        return location;
    }
}

2. (简答题)(Largest row and column) Write a program that randomly fills in 0s and 1s into  a 4-by-4 matrix, prints the matrix, and finds the first row and column with the  most 1s. Here is a sample run of the program: 

0 0 1 1 

0 0 1 1 

1 1 0 1 

1 0 1 0 

The largest row index: 2 

The largest column index: 2

public class Demo19 {
    public static void main(String[] args) {
        int [][]matrix= new int[4][4];
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[i].length; j++) {
                matrix[i][j]=(int)(Math.random()*2);
                System.out.print(matrix[i][j]+"\t");
            }
            System.out.println();
        }
        int maxR=0;
        int maxC=0;
        int row = 0;
        int col=0;
        for (int i = 0; i < matrix.length; i++) {
            int numR=0;
            int numC=0;
            for (int j = 0; j < matrix[i].length; j++) {
                if(matrix[i][j]==1){
                    numR++;
                }
                if(matrix[j][i]==1){
                    numC++;
                }
            }
            if (numR>maxR){
                maxR=numR;
                row = i;
            }
            if(numC>maxC){
                maxC=numC;
                col=i;
            }
        }
        System.out.println("The largest row index: "+row);
        System.out.println("The largest column index: "+col);

    }
}