Recursion in Java

Recursion in Java

递归无出口

1public class RecursionExample1 {
2    public static void p() {
3        System.out.println("hello");
4        p();
5    }
6
7    public static void main(String[] args) {
8        p();
9    }
10}

<div class="collapse" id="RecursionExample1"> \`\`\` Exception in thread "main" java.lang.StackOverflowError \`\`\` </div>

递归有出口

1public class RecursionExample2 {
2    public static int count = 0;
3
4    public static void p() {
5        count++;
6        if (count <= 5) {
7            System.out.println("hello " + count);
8            p();
9        }
10    }
11
12    public static void main(String[] args) {
13        p();
14    }
15}

<div class="collapse" id="RecursionExample2"> \`\`\` hello 1 hello 2 hello 3 hello 4 hello 5 \`\`\` </div>

递归求阶乘

1public class RecursionExample3 {
2    public static int factorial(int n) {
3        if (n == 1) {
4            return 1;
5        } else {
6            return (n * factorial(n - 1));
7        }
8    }
9
10    public static void main(String[] args) {
11        System.out.println("Factorial of 5 is: " + factorial(5));
12    }
13}

<div class="collapse" id="RecursionExample3"> \`\`\` Factorial of 5 is: 120 \`\`\` </div>

Fibonacci 系列

1public class RecursionExample4 {
2    public static int n1 = 0, n2 = 1, n3 = 0;
3
4    public static void printFibonacci(int count) {
5        if (count > 0) {
6            n3 = n1 + n2;
7            n1 = n2;
8            n2 = n3;
9            System.out.print(" " + n3);
10            printFibonacci(count - 1);
11        }
12    }
13
14    public static void main(String[] args) {
15        int count = 15;
16        System.out.print(n1 + " " + n2);
17        printFibonacci(count - 2);
18    }
19}

1public class RecursionExample5 {
2    public static void main(String[] args) {
3        for (int i = 1; i <= 10; i++) {
4            System.out.print(f(i) + " ");
5        }
6        System.out.println();
7        for (int i = 1; i <= 10; i++) {
8            System.out.print(f2(i) + " ");
9        }
10    }
11
12    /**
13     * 递归实现
14     */
15    public static long f(int n) {
16        if (n == 1 || n == 2) {
17            return 1;
18        } else {
19            return f(n - 1) + f(n - 2);
20        }
21    }
22
23    /**
24     * 非递归实现
25     */
26    public static long f2(int n) {
27        int[] a = new int[n + 1];
28        a[0] = 0;
29        a[1] = 1;
30        for (int i = 2; i <= n; i++) {
31            a[i] = a[i - 1] + a[i - 2];
32        }
33        return a[n];
34    }
35}

参考资料

https://www.javatpoint.com/recursion-in-java

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