求1+2＋．．．＋n

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不用if.else.while等一切的条件判断

这题真是涨知识了：

１．　

#include<stdio.h>typedef int (*fun)(int);int f1(int i){    return 0;}int f2(int i){    fun f[2]={ f1,f2 };    return i+f[!!i](i-1);}int main(){    int sum = f2(100);    printf("%d\n",sum);    return 0;}

２．　运用c++的static性质

class Temp{public:      Temp() { ++ N; Sum += N; }      static void Reset() { N = 0; Sum = 0; }      static int GetSum() { return Sum; }private:      static int N;      static int Sum;};int Temp::N = 0;int Temp::Sum = 0;int solution1_Sum(int n){      Temp::Reset();      Temp *a = new Temp[n];      delete []a;      a = 0;      return Temp::GetSum();}

３．

template <int n> struct solution4_Sum{      enum Value { N = solution4_Sum<n - 1>::N + n};};template <> struct solution4_Sum<1>{      enum Value { N = 1};};

转自

http://zhedahht.blog.163.com/blog/static/2541117420072915131422/

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