>[success] # 遞歸練習 * 遞歸本質就是指在方法體的內部**直接或間接調用當前方法自身**的形式 * 遞歸必須有遞歸的規律以及**退出條件** >[danger] ##### 實現數n的階乘 ~~~ public class SumTest { // 非遞歸 int factorial(int num) { int sum = 1; for (int i = 1; i <= num; i++) { sum *= i; } return sum; } // 使用遞歸 int recursionFactorial(int num) { if (num == 1) { return 1; } return num * recursionFactorial(num - 1); } public static void main(String[] args) { SumTest sumTest = new SumTest(); int a = sumTest.factorial(5); // 120 int b = sumTest.recursionFactorial(5); // 120 System.out.println(a + "," + b); } } ~~~ >[danger] ##### 斐波那契數列 * 非遞歸思路  ~~~ public class SumTest { // 非遞歸 利用指針 int fibonacci(int index) { int a = 1; int b = 1; int c = b; while (index >= 3) { b = a + c; a = c; c = b; index--; } return b; } // 使用遞歸 int recursionFibonacci(int index) { if (index == 1 || index == 2) { return 1; } return recursionFibonacci(index - 1) + recursionFibonacci(index - 2); } public static void main(String[] args) { SumTest sumTest = new SumTest(); int a = sumTest.fibonacci(6); // 8 int b = sumTest.recursionFibonacci(6); // 8 System.out.println(a + "," + b); } } ~~~