插入（+、-、空格）完成的等式：1 2 3 4 5 6 7 8 9=N

#include<iostream> 

#include<cstdio> 

using namespace std; 

   

int ops[21]; 

const char sym[3] = {'+', '-', ' '}; 

int result , num; 

   

void dfs(int layer, int currentResult, int lastOp, int lastSum) 

{ 

    lastSum *= (layer > 9) ? 100 : 10; 

    lastSum += layer; 

    if(layer == 9) 

    { 

        currentResult += (lastOp) ? (-1 * lastSum) : lastSum; 

        if(currentResult == result) 

        { 

            ++num; 

            printf("1"); 

            for(int i = 2 ; i <= 9 ; ++i) 

            { 

                if(sym[ops[i-1]] != ' ') 

                    printf(" %c ", sym[ops[i-1]]); 

                printf("%d", i); 

            } 

            printf(" = %d\n" , result); 

        } 

        return; 

    } 

    ops[layer] = 2; 

    dfs(layer + 1 , currentResult , lastOp , lastSum);   //Continue 

    currentResult += (lastOp)? (-1 * lastSum) : lastSum; 

    ops[layer] = 0; 

    dfs(layer + 1 , currentResult , 0 , 0);  //Plus 

    ops[layer] = 1; 

    dfs(layer + 1 , currentResult , 1 , 0);  //Minus 

}

int main(void) 

{ 

    while(scanf("%d", &result) != EOF) 

    { 

        num = 0; 

        dfs(1 , 0 , 0 , 0); 

        printf("%d\n", num); 

    } 

    return0; 

}