用递归方法求和值

Question

我正在尝试使用递归方法对文本文件中的值求和，文本文件中的值由分号分隔。文本文件中的数据是这样存储的：

7708190034; Environment; 10500; Schools; 8000; Health care; 9500
9609131234; Environment; 20000; Schools; 20000; Health care; 18000

假设我想对环境的值求和，这样在这种情况下输出将类似于 "Sum for environment: 30500" 等。换句话说，对于环境，我想首先阅读环境部分行（值 10500）然后读取下一行并将找到的值（在本例中为 20000）添加到第一行，最后打印出它的总和。求和应该用递归的方法来完成。目前我使用以下代码：

/*Main method:*/
public static void main(String[] args) throws IOException {
    //Invoke method to sum environments through recursive method:
    readEnvironment();
}

/*Method to read environment values:*/
static void readEnvironment() throws IOException {
    List<Integer> environmentsum = new ArrayList<>();
    File file = new File("sums.txt");

    FileReader fr = new FileReader(file);
    BufferedReader br = new BufferedReader(fr);

    // Read the first line from the file
    String s = br.readLine();
    // As long as we have not reached the end of the file...
    while (s != null) {
        // Split the string read from the file by the separator ;
        String[] data = s.split(";");

        //As long as the string has 6 parts...
        if (data.length == 6) {
            // We know that the second part in the line is the value for an environment:
            int number = Integer.parseInt(data[2]);
            //Add the found number to the array:
            environmentsum.add(number);
        }

        int sum = 0;
        //Invoke recursive method:
        sum = sum(environmentsum, 0);
        System.out.println("Sum for environment: " + sum);
        //Read next line:
        s = br.readLine();
    }
    br.close();
}

/*Recursive method to sum the values:*/
static int sum(List<Integer> t, int index) {
    //If there are no elements in the array:
    if (index == t.size()) {
        return 0;
    }
    int sum = t.get(index) + sum(t, index + 1);
    return sum;
}

目前我只得到这样的输出：

Sum for environment: 0
Sum for environment: 0
Sum for environment: 0

但期望的结果应该是这样的：

Sum for environment: 30500

我错过了什么或做错了什么？

Answer 1

根据您的格式，

String[] data = s.split(";"); 会得到 data.length 等于 7：

7708190034; Environment; 10500; Schools; 8000; Health care; 9500

所以它永远不会进入 if (data.length == 6) 块，并且 environmentsum 总是空的

你可以把它改成 if (data.length == 7)

Answer 2

查看此代码：

//Add the found number to the array:
andelarsk.add(andel);

您要添加到 andelarsk 列表（仅当您的行中有 6 列以“;”分隔时），并且要向 sum 方法传递 environmentsum

sum = sum(environmentsum, 0);

此外，每一行都会调用这个求和方法，你会得到如下内容：

Sum for environment: ..
Sum for environment: ..
Sum for environment: ..

我建议您在填充列表中的所有环境值后调用递归方法和打印语句 post while 循环。

Answer 3

将每行中的字段数与您要检查的数量进行比较：

if (data.length == 6) {

你可以

if (data.length > 2) {

Answer 4

我自己用下面的代码解决了：

public static void readEnvironment() throws IOException {

    List<Integer> all = new ArrayList<>();
    File file = new File("test.txt");
    FileReader fr = new FileReader(file);
    BufferedReader br = new BufferedReader(fr);
    String s = br.readLine();

    while (s != null) {
        String[] data = s.split(";");
        //We know that the second part in a line is the amount for environment:
        int a = Integer.parseInt(data[2]);
        s = br.readLine();
        all.add(a);
    }
    br.close();

    int sum = 0;
    //Invoke the sum method:
    sum = sum(all, 0);
    System.out.println("Sum for environment: " + sum);
}

用递归方法求和值

sum values with recursive method

java

recursion

sum