UVa10400

表示式形式，采用深搜。和24点类似。不过比24点简单一点，采用一个状态判重数组

注意回溯的时候，因为是对每一次cur进行数字运算。

所以当vis[cur][sum] = 1时回溯回来的时候不要改其被访问的状态。

因为不管怎样只要sum在cur处被运算到了都是一样的，所以不要改回来。

一开始在dfs(cur+1)后加了句vis[cur][sum] = 0;

结束TLE了。

后面看的解体报告才改过来AC了。。

AC代码：

#include <iostream>#include <cstring>//#include <stdio.h>using namespace std;const int MAX_NUMBER = 101;const int MAX_STATE = 65000;const int OFF_SET =32001;int numbers[MAX_NUMBER];int vis[MAX_NUMBER][MAX_STATE];int has_found;char temp_symbols[MAX_NUMBER];char ans_symbols[MAX_NUMBER];int k_number;int target_number;int result;void dfs(int cur) {    if(cur >= k_number) {        if (result == target_number) {            has_found = 1;            memcpy(ans_symbols,temp_symbols,sizeof(ans_symbols));        }        return ;    }    if (has_found)        return ;    else {        if (!has_found && (result + numbers[cur]) <= 32000 && (result + numbers[cur]) >= -32000 && !vis[cur][result + numbers[cur] + OFF_SET]) {            temp_symbols[cur - 1] = '+';            result += numbers[cur];            vis[cur][result + OFF_SET] = 1;            dfs(cur + 1);            result -= numbers[cur];        }        if (!has_found && (result - numbers[cur]) <= 32000 && (result - numbers[cur]) >= -32000 && !vis[cur][result - numbers[cur] + OFF_SET]) {            temp_symbols[cur - 1] = '-';            result -= numbers[cur];            vis[cur][result + OFF_SET] = 1;            dfs(cur + 1);            result += numbers[cur];        }        if (!has_found && (result * numbers[cur]) <= 32000 && (result * numbers[cur]) >= -32000 && !vis[cur][result * numbers[cur]] + OFF_SET) {            temp_symbols[cur - 1] = '*';            result *= numbers[cur];            vis[cur][result + OFF_SET] = 1;            dfs(cur + 1);            result /= numbers[cur];        }        if (!has_found && (result % numbers[cur]) == 0 && !vis[cur][result / numbers[cur] + OFF_SET]) {            temp_symbols[cur - 1] = '/';            result /= numbers[cur];            vis[cur][result + OFF_SET] = 1;            dfs(cur + 1);            result *= numbers[cur];        }    }}int main() {    //freopen("input.txt","r",stdin);    int test_case;    cin >> test_case;    while (test_case--) {        cin >> k_number;        has_found = 0;        memset(vis,0,sizeof(vis));        for (int i = 0;i < k_number; i++) {            cin >> numbers[i];        }        cin >> target_number;        result = numbers[0];        vis[0][result+OFF_SET] = 1;        dfs(1);        if (!has_found) {            cout << "NO EXPRESSION" << endl;        } else {            for (int i = 0; i < k_number; i++) {                cout << numbers[i];                if (i != k_number - 1)                cout << ans_symbols[i];            }            cout << "=" << target_number;            cout << endl;        }    }    return 0;}