Double Factorial

ID: 771; easy; 二阶阶乘

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Solution 1 (Java)

public class Solution {
    /**
     * @param n: the given number
     * @return:  the double factorial of the number
     */
    public long doubleFactorial(int n) {
        if (n == 0 || n == 1) return 1;
        return (long)n * doubleFactorial(n - 2);
    }
}

Notes

• By definition of double factorial, the result is immediate.