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Palindrome_Permutation_II.cpp
52 lines (49 loc) · 1.48 KB
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Palindrome_Permutation_II.cpp
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class Solution {
#define MAX 256
void generatePalindromesImpl(int left, int right, vector<int>& freq, string& solution, vector<string>& result) {
if(left > right) {
result.push_back(solution);
return;
}
for(int i = 0; i < MAX; ++i) {
if(freq[i] >= 2) {
solution[left] = solution[right] = (char)i;
freq[i] -= 2;
generatePalindromesImpl(left + 1, right - 1, freq, solution, result);
freq[i] += 2;
} else if(freq[i] == 1 and left == right) {
// freq[i]--;
solution[left] = (char)i;
generatePalindromesImpl(left + 1, right - 1, freq, solution, result);
// freq[i]++;
}
}
}
public:
vector<string> generatePalindromes(string s) {
vector<string> result;
int n = s.length();
vector<int> freq(MAX, 0);
for(int i = 0; i < n; ++i) {
freq[s[i]]++;
}
int oddParity = 0;
for(int i = 0; i < MAX; ++i) {
if(freq[i] & 1) {
oddParity++;
}
}
if(n & 1) {
if(oddParity != 1) {
return result;
}
} else {
if(oddParity > 0) {
return result;
}
}
string solution = s;
generatePalindromesImpl(0, n - 1, freq, solution, result);
return result;
}
};