Question

我想做的是：

我有一个值列表，我想列出它们中的每三个。例如：

我有：

"one", "two", "three", "four", "five"

我想打印以下内容：

one two three
one two four
one four five
two three four
two three five
and so on

你明白了，我想要每三个值（不按顺序排序）

我做的是：

import java.util.*;

public class Solution {
    public static void main(String args[]) {
        String[] people = new String[] { "one", "two", "three", "four",
                "five" };
        Solution s = new Solution();
        s.solve(people, 3, new LinkedList<>(), 0);
    }

    public void solve(String[] people, int n, List<String> data, int i) {
        if (data.size() == n) {
            System.out.println(data.toString());

        } else if (i < people.length) {
            String value = people[i];
            solve(people, n, data, i + 1);
            data.add(value);
            solve(people, n, data, i + 1);
        }
    }
}

你可以运行它：

我的问题是打印出来了：

[五，四，五]

这显然是错误的，怎么能打印两个相同的值？在我的代码中，我添加了一次值，我不再添加它

你可以帮忙吗？

Answer 1

怎么能打印两个相同的值？

原因在于您已将代码放入代码中：

else if (i < people.length)

带您完成执行框架：

solve(people, n, data, i + 1); 

// (1) this recurses until i = 4(which is less than the length=5)
// for the next iteration the condition i<people.length wouldn't be satisfied

// (2) hence this is called
data.add(value);  // data now has "five"

// since when the previous recursion ended i=4 (callee)
solve(people, n, data, i + 1); 
// (3) this recurses again and finds the same condition of not being able to recurse more
// hence data gets value = "four"

使用i+1，它会旋转回（1）并打印＆＃34;五＆＃34;试。

PS ：如果之后会发生什么，我会留给你弄清楚。

提示：执行不会在这里结束。 提示++ ：递归回溯。

Answer 2

public void solve(String[] people, int n, List<String> data, int i) {
    if (data.size() == n) {
        System.out.println(data.toString());
        return;
    }

    if (i == people.length) {
        return;
    }

    data.add(people[i]);
    solve(people, n, data, i + 1);
    data.remove(people[i]);
    solve(people, n, data, i + 1);
}

输出

[one, two, three]
[one, two, four]
[one, two, five]
[one, three, four]
[one, three, five]
[one, four, five]
[two, three, four]
[two, three, five]
[two, four, five]
[three, four, five]

什么程序打印错误的reutls

2 个答案: