Recursion in Java
递归无出口
public class RecursionExample1 {
public static void p() {
System.out.println("hello");
p();
}
public static void main(String[] args) {
p();
}
}
运行结果
```
Exception in thread "main" java.lang.StackOverflowError
```
递归有出口
public class RecursionExample2 {
public static int count = 0;
public static void p() {
count++;
if (count <= 5) {
System.out.println("hello " + count);
p();
}
}
public static void main(String[] args) {
p();
}
}
运行结果
```
hello 1
hello 2
hello 3
hello 4
hello 5
```
递归求阶乘
public class RecursionExample3 {
public static int factorial(int n) {
if (n == 1) {
return 1;
} else {
return (n * factorial(n - 1));
}
}
public static void main(String[] args) {
System.out.println("Factorial of 5 is: " + factorial(5));
}
}
运行结果
```
Factorial of 5 is: 120
```
Fibonacci 系列
public class RecursionExample4 {
public static int n1 = 0, n2 = 1, n3 = 0;
public static void printFibonacci(int count) {
if (count > 0) {
n3 = n1 + n2;
n1 = n2;
n2 = n3;
System.out.print(" " + n3);
printFibonacci(count - 1);
}
}
public static void main(String[] args) {
int count = 15;
System.out.print(n1 + " " + n2);
printFibonacci(count - 2);
}
}
运行结果
```
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377
```
public class RecursionExample5 {
public static void main(String[] args) {
for (int i = 1; i <= 10; i++) {
System.out.print(f(i) + " ");
}
System.out.println();
for (int i = 1; i <= 10; i++) {
System.out.print(f2(i) + " ");
}
}
/**
* 递归实现
*/
public static long f(int n) {
if (n == 1 || n == 2) {
return 1;
} else {
return f(n - 1) + f(n - 2);
}
}
/**
* 非递归实现
*/
public static long f2(int n) {
int[] a = new int[n + 1];
a[0] = 0;
a[1] = 1;
for (int i = 2; i <= n; i++) {
a[i] = a[i - 1] + a[i - 2];
}
return a[n];
}
}
运行结果
```
1 1 2 3 5 8 13 21 34 55
1 1 2 3 5 8 13 21 34 55
```
参考资料