[Microsoft面试]题目：求1+2+…+n，
要求不能使用乘除法、for、while、if、else、switch、case等关键字以及条件判断语句（A?B:C）。 1+..+n=n*(n+1)/2=(n^2+n)/2it is easy to get x/2, so the problem is to get n^2though no if/else is allowed, we can easilly go around using short-pass.using macro to make it fancier:#define T(X, Y, i) (Y & (1<<i)) && X+=(Y<<i)intfoo(int n){int r=n;T(r, n, 0); T(r, n,1); T(r, n, 2); … T(r, n, 31);return r >> 1;}
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