1, 2, 3...N这N个数，中间用空白分隔。在空白处填上加号或者减号,求出一共有多少种加运算符的方法使得整个表达式的值为0，并输出所有的方案-1, 2, 3 ... N all N numbers, separated by white space. Fill in the blank plus or minus sign, so that the entire expression uates to 0, and output all possible expressions