剑指Offer46 求1+2+...+n

 1 /*************************************************************************
 2     > File Name: 46_Accumulate.c
 3     > Author: Juntaran
 4     > Mail: JuntaranMail@gmail.com
 5     > Created Time: 2016年09月04日 星期日 21时18分28秒
 6  ************************************************************************/
 7  
 8 #include <stdio.h>
 9 
10 // 函数指针法求1+2+...+n
11 typedef unsigned int (*fun)(unsigned int);
12 
13 unsigned int sum_T(int n)
14 {
15     return 0;
16 }
17 
18 int Sum1(int n)
19 {
20     static fun f[2] = {sum_T, Sum1};
21     return n + f[!!n](n-1);
22 }
23 
24 // 递归
25 int Sum2(int n)
26 {
27     int sum = n;
28     int ans = (n>0) && (sum+=Sum2(n-1));
29     return sum;
30 }
31 
32 int main()
33 {
34     int n = 7;
35     int ret1 = Sum1(n);
36     int ret2 = Sum2(n);
37     printf("ret1 is %d\n", ret1);
38     printf("ret2 is %d\n", ret2);
39     
40     return 0;
41 }