请问我的代码有什么问题，题目如下

Question

Common permutation Time Limit: 1000ms, Special Time Limit:2500ms, Memory Limit:32768KBTotal submit users: 1060, Accepted users: 951Problem 10048 : No special judgement Problem descriptionGiven two strings of lowercase letters, a and b, print the longest string x of lowercase letters such that there is a permutation of x that is a subsequence of a and there is a permutation of x that is a subsequence of b.InputInput consists of pairs of lines. The first line of a pair contains a and the second contains b. Each string is on a separate line and consists of at most 1,000 lowercase letters. OutputFor each subsequent pair of input lines, output a line containing x. If several x satisfy the criteria above, choose the first one in alphabetical order. Sample Inputpretty women walking down the streetSample Outpute nw etProblem SourceUAL 1999我的代码如下 #include<iostream>#include<string> using namespace std;int main(){string a,b;while(cin>>a>>b){int c[26]={0},d[26]={0};int  n1=a.length(),n2=b.length();for(int i=0;i<n1;i++){if(c[(int)a[i]-97]==0){c[(int)a[i]-97]=1;}}for(int i=0;i<n2;i++){if(d[(int)b[i]-97]==0){d[(int)b[i]-97]=1;}}for(int i=0;i<26;i++){if(c[i]!=0&&d[i]!=0)cout<<char(i+97);}cout<<endl;}}

Answer 1

while(cin>>a>>b)这句别用cin，用gets