题目很简单，自己都说了让我们暴搜。
运算符最多 8 个，每个 3 种，果然大家都是 0.000 sec 就 AC 了。
我这边也写得丑丑的。递归搜索（注意下 ascii 码顺序）。对表达式进行解析计算（我也不知道我怎么写的这一段，竟然就通过了），记录下左边的值、操作符、右边的值，如果下一个操作符是空格，就给右边添一位，是加减就把上次操作做了，记录新的操作符和右边。
/*
ID:
LANG: C++
TASK: zerosum
*/
#include <cstdio>
#include <cstdlib>
int N;
FILE *fout;
char operations[8];
int parse(){
char op = '+';
int pre = 0, post = 1;
for(int n = 2; n <= N; n ++){
if(operations[n - 2] == ' '){
post = post * 10 + n;
}else{
pre = (op == '+'? pre + post: pre - post);
op = operations[n - 2];
post = n;
}
}
pre = (op == '+'? pre + post: pre - post);
return pre;
}
void search(int i){
if(i == N - 1){
if(parse() == 0){
for(int i = 1; i < N; i ++)
fprintf(fout, "%d%c", i, operations[i - 1]);
fprintf(fout, "%d\n", N);
}
return;
}
operations[i] = ' '; search(i + 1);
operations[i] = '+'; search(i + 1);
operations[i] = '-'; search(i + 1);
}
int main(){
FILE *fin = fopen("zerosum.in", "r");
fout = fopen("zerosum.out", "w");
fscanf(fin, "%d", &N);
search(0);
return 0;
}
第一次提交 AC：
Compiling...
Compile: OK
Executing...
Test 1: TEST OK [0.000 secs, 4176 KB]
Test 2: TEST OK [0.000 secs, 4176 KB]
Test 3: TEST OK [0.000 secs, 4176 KB]
Test 4: TEST OK [0.000 secs, 4176 KB]
Test 5: TEST OK [0.000 secs, 4176 KB]
Test 6: TEST OK [0.000 secs, 4176 KB]
Test 7: TEST OK [0.000 secs, 4176 KB]
All tests OK.
