Kick Start 2022 Round A 2022 Palindrome Free Strings
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| #include <bits/stdc++.h>
using namespace std;
bool oddpal(string& s, int r) {
int l = r - 4;
if(l < 0) return false;
while(l < r)
if(s[l++] != s[r--]) return false;
return true;
}
bool evenpal(string& s, int r) {
int l = r - 5;
if(l < 0) return false;
while(l < r)
if(s[l++] != s[r--]) return false;
return true;
}
bool manacher(string& s) {
string p = "#";
for(auto ch : s) {
p += string(1,ch) + '#';
}
vector<int> dp(p.length());
int l = 0, r = -1;
for(int i = 1; i < p.length() - 1; i++) {
dp[i] = max(0, min(r - i, (l + r - i >= 0 ? dp[l + (r - i)] : -1)));
while(i - dp[i] >= 0 and p[i + dp[i]] == p[i - dp[i]])
dp[i]++;
if(r < i + dp[i]) {
l = i - dp[i];
r = i + dp[i];
}
if(p[i] != '#' and dp[i] >= 5) return false;
else if(p[i] == '#' and dp[i] >= 6) return false;
}
return true;
}
bool solve(string& s, int i = 0) {
if(i == s.length()) {
return manacher(s);
}
if(s[i] != '?') {
return !oddpal(s,i) and !evenpal(s,i) and solve(s, i + 1);
} else {
s[i] = '0';
if(!oddpal(s,i) and !evenpal(s,i) and solve(s, i + 1))
return true;
s[i] = '1';
if(!oddpal(s,i) and !evenpal(s,i) and solve(s, i + 1))
return true;
s[i] = '?';
return false;
}
}
int main() {
int t;
cin>>t;
for(int i = 1; i <= t; i++) {
int n;
string s;
cin>>n>>s;
string res = solve(s) ? "POSSIBLE" : "IMPOSSIBLE";
cout<<"Case #"<<i<<": "<<res <<endl;
}
return 0;
}
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