64 lines
1.6 KiB
C++
64 lines
1.6 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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/*
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aabaaab
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答案：
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[0,1,0,1,2,2,3]
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*/
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//朴素版本求字符串的前缀函数
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vector<int> prefix_function1(string s) {
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int n = (int)s.length();
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vector<int> pi(n);
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for (int i = 1; i < n; i++)
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for (int j = i; j >= 0; j--)
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if (s.substr(0, j) == s.substr(i - j + 1, j)) {
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pi[i] = j;
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break;
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}
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return pi;
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}
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// 第一轮优化后的版本
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vector<int> prefix_function2(string s) {
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int n = (int)s.length();
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vector<int> pi(n);
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for (int i = 1; i < n; i++)
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for (int j = pi[i - 1] + 1; j >= 0; j--) // improved: j=i => j=pi[i-1]+1
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if (s.substr(0, j) == s.substr(i - j + 1, j)) {
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pi[i] = j;
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break;
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}
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return pi;
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}
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// 第二轮优化后的版本
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vector<int> prefix_function3(string s) {
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int n = (int)s.length();
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vector<int> pi(n);
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for (int i = 1; i < n; i++) {
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int j = pi[i - 1];
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while (j > 0 && s[i] != s[j]) j = pi[j - 1];
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if (s[i] == s[j]) j++;
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pi[i] = j;
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}
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return pi;
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}
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int main() {
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string s = "aabaaab";
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vector<int> res = prefix_function1(s);
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for (int i = 0; i < (int)res.size(); i++)
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cout << res[i] << " ";
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puts("");
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res = prefix_function2(s);
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for (int i = 0; i < (int)res.size(); i++)
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cout << res[i] << " ";
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puts("");
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res = prefix_function3(s);
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for (int i = 0; i < (int)res.size(); i++)
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cout << res[i] << " ";
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puts("");
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return 0;
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} |