Palindrome CodeForces - 1512C

You are given a string s consisting of the characters ‘0’, ‘1’, and ‘?’. You need to replace all the characters with ‘?’ in the string s by ‘0’ or ‘1’ so that the string becomes a palindrome and has exactly a characters ‘0’ and exactly b characters ‘1’. Note that each of the characters ‘?’ is replaced independently from the others.

A string t of length n is called a palindrome if the equality t[i]=t[n−i+1] is true for all i (1≤i≤n).

For example, if s=“01???0”, a=4 and b=4, then you can replace the characters ‘?’ in the following ways:

“01011010”;
“01100110”.
For the given string s and the numbers a and b, replace all the characters with ‘?’ in the string s by ‘0’ or ‘1’ so that the string becomes a palindrome and has exactly a characters ‘0’ and exactly b characters ‘1’.

Input
The first line contains a single integer t (1≤t≤104). Then t test cases follow.

The first line of each test case contains two integers a and b (0≤a,b≤2⋅105, a+b≥1).

The second line of each test case contains the string s of length a+b, consisting of the characters ‘0’, ‘1’, and ‘?’.

It is guaranteed that the sum of the string lengths of s over all test cases does not exceed 2⋅105.

Output
For each test case, output:

“-1”, if you can’t replace all the characters ‘?’ in the string s by ‘0’ or ‘1’ so that the string becomes a palindrome and that it contains exactly a characters ‘0’ and exactly b characters ‘1’;
the string that is obtained as a result of the replacement, otherwise.
If there are several suitable ways to replace characters, you can output any.

Example

Input

9
4 4
01???0
3 3
???
1 0
?
2 2
0101
2 2
01?0
0 1
0
0 3
1?1
2 2
?00?
4 3
??010?0

Output

01011010
-1
0
-1
0110
-1
111
1001
0101010

题意：

给你a个0，b个1，一个字符串，将给的字符串中的？替换为0或1，使这个字符串为有a个0，b个1的回文串，如果可以，就输出回文串，不可以，输出-1

思路：

模拟+思维 =AC（还有n次的WA）

代码：

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
char s[400010];
int pal(char a[],int l)
{
    for(int i=0; i<l; i++)
    {
        if(a[i]!=a[l-1-i])
            return 0;
    }
    return 1;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int a,b;
        scanf("%d %d",&a,&b);
        scanf("%s",s);
        int l=strlen(s);
        int num0=0,num1=0;
        for(int i=0; i<l; i++)
        {
            if(s[i]=='0')
                num0++;
            else if(s[i]=='1')
                num1++;
        }
        if(num0>a||num1>b)
            printf("-1\n");
        else
        {
            a=a-num0;
            b=b-num1;
            int f=0;
            for(int i=0; i<=l/2; i++)
            {
                if(s[i]=='0')
                {
                    if(s[l-1-i]=='?')
                    {
                        if(a>=1)
                        {
                            s[l-1-i]='0';
                            a--;
                        }
                    }
                }
                else if(s[i]=='1')
                {
                    if(s[l-1-i]=='?')
                    {
                        if(b>=1)
                        {
                            s[l-1-i]='1';
                            b--;
                        }
                    }
                }
                else if(s[i]=='?')
                {
                    if(s[l-1-i]=='0')
                    {
                        if(a>=1)
                        {
                            s[i]='0';
                            a--;
                        }
                    }
                    else if(s[l-1-i]=='1')
                    {
                        if(b>=1)
                        {
                            s[i]='1';
                            b--;
                        }
                    }
                }
            }
            for(int i=0; i<=l/2; i++)
            {
                if(s[i]=='?')
                {
                    if(s[l-1-i]=='?')
                    {
                        if(l-1-i==i)
                        {
                            if(a>=1)
                            {
                                s[i]='0';
                                a--;
                            }
                            else if(b>=1)
                            {
                                s[i]='1';
                                b--;
                            }
                        }
                        else if(a>=2)
                        {
                            s[i]='0';
                            s[l-1-i]='0';
                            a-=2;
                        }
                        else if(b>=2)
                        {
                            s[i]='1';
                            s[l-1-i]='1';
                            b-=2;
                        }
                    }
                }
            }
            for(int i=0; i<l; i++)
            {
                if(s[i]=='?')
                {
                    f=1;
                    break;
                }
            }
            if(f==1||pal(s,l)==0||a||b)
                printf("-1\n");
            else
                printf("%s\n",s);
        }
    }
    return 0;
}