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Copy path5.LongestPalindromicSubstring.cpp
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executable file
·134 lines (128 loc) · 3.59 KB
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/*
@filename LongestPalindromicSubstring.cpp
@author caonan
@date 2022-04-04 14:50:06
@reference leetcode
@url https://leetcode-cn.com/problems/longest-palindromic-substring/
@brief 给你一个字符串 s，找到 s 中最长的回文子串。
*/
#include <assert.h>
#include <limits.h>
#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <map>
#include <vector>
using namespace std;
class Solution {
public:
// 中心扩展法
string longestPalindrome(string s) {
string t = "#";
for (const auto& c : s) {
t += c;
t += "#";
}
string longest_str;
for (int i = 1; i < t.length() - 1; i++) {
int left = i;
int right = i;
while (left >= 0 && right < t.length()) {
if (t[left] == t[right]) {
if (longest_str.length() < right - left + 1) {
longest_str = t.substr(left, right - left + 1); // 每次都有拷贝，是否记住下标索引更好点？
}
} else {
break;
}
left--;
right++;
}
}
auto no_space_end = std::remove(longest_str.begin(), longest_str.end(), '#');
longest_str.erase(no_space_end, longest_str.end());
return longest_str;
}
// 用左右下标记录最大回文子串，减少字符串拷贝
string longestPalindrome1(string s) {
string t = "#";
for (const auto& c : s) {
t += c;
t += "#";
}
int max_len = INT_MIN;
int left_max = 0;
int right_max = 0;
for (int i = 1; i < t.length() - 1; i++) {
int left = i;
int right = i;
while (left >= 0 && right < t.length()) {
if (t[left] == t[right]) {
if (max_len < right - left + 1) {
max_len = right - left + 1;
left_max = left;
right_max = right;
}
} else {
break;
}
left--;
right++;
}
}
string longest_str = t.substr(left_max, right_max - left_max + 1);
auto noSpaceEnd = std::remove(longest_str.begin(), longest_str.end(), '#');
longest_str.erase(noSpaceEnd, longest_str.end());
return longest_str;
}
// 空间复杂度o(1),不借助额外字符串修改
string longestPalindrome2(string s) {
int max_len = INT_MIN;
int left_max = 0;
int right_max = 0;
for (int i = 0; i < s.length(); i++) {
int left = i;
int right = i;
auto calc = [&]() {
while (left >= 0 && right < s.length()) {
if (s[left] == s[right]) {
if (right - left + 1 > max_len) {
max_len = right - left + 1;
left_max = left;
right_max = right;
}
} else {
break;
}
left--;
right++;
}
};
calc();
left = i;
right = i + 1;
calc();
}
string longest_str = s.substr(left_max, right_max - left_max + 1);
return longest_str;
}
// todo:进阶，Manacher
};
int main() {
Solution s;
cout << s.longestPalindrome("babad") << endl;
cout << s.longestPalindrome("a") << endl;
cout << s.longestPalindrome("") << endl;
cout << s.longestPalindrome("cbbd") << endl;
cout << "-----------------" << endl;
cout << s.longestPalindrome1("babad") << endl;
cout << s.longestPalindrome1("a") << endl;
cout << s.longestPalindrome1("") << endl;
cout << s.longestPalindrome1("cbbd") << endl;
cout << "-----------------" << endl;
cout << s.longestPalindrome2("babad") << endl;
cout << s.longestPalindrome2("a") << endl;
cout << s.longestPalindrome2("") << endl;
cout << s.longestPalindrome2("cbbd") << endl;
return 0;
}