【HDOJ6342】Expression in Memories（模拟）

题意：

给定一个由0123456789+* ?组成的表达式，其中？可以被改为任意其它字符，问修改问号后是否有方案使得表达式合法

len<=5e2，sumlen<=1e5

思路：

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <algorithm>
#include <iostream>
#include <ctype.h>
#include <limits.h>
#include <set>
#include <map>
#include <vector>
#include <stack>
#include <queue>
#include <list>
#define left (now<<1)
#define right ((now<<1)+1)
#define mid ((l+r)>>1)
#define fst first
#define snd second
using namespace std;
typedef long long lint;

const int MAXN = 5e2 + 10;

char str[MAXN];
int n;
bool ok[MAXN];

void init(){
    for(int i = 0; i < MAXN; ++i){
        str[i] = '';
    }
}

int main(){
    int t; scanf("%d",&t);
    while(t--){
        init(); scanf("%s",str); int len = strlen(str); bool zero = false;
        memset(ok,false,sizeof(ok));
        for(int i = 0; i < len; ++i){
            if(str[i] == '?'){
                str[i] = '1'; ok[i] = true;
            }
        }

        bool can = true; zero = false;
        if(str[0] == '+' || str[0] == '*' || str[len - 1] == '+' ||str[len - 1] == '*'){
            can = false;
        }
        for(int i = 0; i < len - 1; ++i){
            if((str[i] == '+' || str[i] == '*') && (str[i + 1] == '*' || str[i + 1] == '+')){
                can = false; break;
            }
        }
        for(int i = 0; i < len; ++i){
            if(isdigit(str[i]) && zero){
                if(ok[i] == false){
                    can = false; break;
                }else{
                    str[i] = '+';
                }
            }
            if(str[i] == '0' && (i == 0 || !isdigit(str[i - 1]))){
                zero = true;
            }else{
                zero = false;
            }
        }
        if(str[0] == '+' || str[0] == '*' || str[len - 1] == '+' ||str[len - 1] == '*'){
            can = false;
        }
        for(int i = 0; i < len - 1; ++i){
            if((str[i] == '+' || str[i] == '*') && (str[i + 1] == '*' || str[i + 1] == '+')){
                can = false; break;
            }
        }
        if(can){
            printf("%s
",str);
        }else{
            printf("IMPOSSIBLE
");
        }
    }
    return 0;
}