Question

有人向我指出，下面的陈述不是递归。我认为递归只意味着它会调用自己直到找到答案。什么会导致这种递归？

public static double totalDistance(int[] x, int[] y, String[] city, int i){

    double xSub = x[i] - x[i-1];
    double ySub = y[i] - y[i-1];
    double distance = Math.pow(xSub, 2) + Math.pow(ySub, 2);
    distance = Math.round(Math.sqrt(distance));
    System.out.println("Distance From " + city[i] + " to " + city[i-1] + " is " + distance + " miles.");

   if (i == 1){
       return distance;  
   }
   else {
      return distance+totalDistance(x,y,city, i-1);
   }
}

以下是完整的代码，以防任何人对发生的事情感到好奇......

import java.util.Scanner;
class distance {


public static void main(String[] args) {

    System.out.println("Welcome to Travel Bliss Distance Calculator!");
    Scanner input = new Scanner(System.in);
    int[] x = new int[5];
    int[] y = new int[5];
    String[] city = new String[5];


    int i=0;
    for (i=0; i < 5;i++){
        System.out.println("Enter City>>");
        city[i] = input.next();
        System.out.println("Enter X Coordinates>>");
        x[i] = input.nextInt();
        System.out.println("Enter Y Coordinates>>");
        y[i] = input.nextInt();
        System.out.println("You Entered: " + city[i] + " with Coordinates: (" + x[i] + "," + y[i] + ") ");


    }
    i = i-1;
    System.out.println("============================================================");

    System.out.println("Calculating Distance Between: " + city[0] +", " + city[1] + ", " + city[2] + ", " + city[3] + ", " + city[4]+" >>>");
    System.out.println("TOTAL of: "+ totalDistance(x, y, city, i)+ " miles.");

}


public static double totalDistance(int[] x, int[] y, String[] city, int i){

    double xSub = x[i] - x[i-1];
    double ySub = y[i] - y[i-1];
    double distance = Math.pow(xSub, 2) + Math.pow(ySub, 2);
    distance = Math.round(Math.sqrt(distance));
    System.out.println("Distance From " + city[i] + " to " + city[i-1] + " is " + distance + " miles.");

   if (i == 1){
       return distance;  
   }
   else {
      return distance+totalDistance(x,y,city, i-1);
   }
}
}

Answer 1

totalDistance（...）函数确实是递归的（因为它自己调用）。

Answer 2

它是递归 - 它们可能意味着什么（或者你误解了）是它不是“尾递归”。

这是递归的一个子集，非常简单，可以优化为一个简单的循环（尽管Java还没有这样做）。要进行尾递归，您必须返回递归调用的结果 - 在您的情况下，首先添加它。

Answer 3

看起来像是递归给我。谁告诉你这不是？

Answer 4

它是递归的。可能批评者认为迭代（循环）版本过于紧密。

可能然后期待，不是从头到尾经过列表，而是选择中间城市，计算从开始到该城市以及从该城市到结束的距离并添加。将计算距离的每一半，调用相同的函数。

被告知我的代码不是递归...寻找指导为什么不！

4 个答案: