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string_compare.cpp
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string_compare.cpp
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// string_compare.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//
#include <iostream>
#include<time.h>
#include<algorithm>
#include<string>
using namespace std;
int kmp(char* s1, char* s2,int len1,int len2) {
int* nxt = new int[len2 + 10];
nxt[0] = -1; nxt[1] = 0;
for (int i = 2, j = 0; i < len2; i++) {
if (s2[i - 1] == s2[j]) nxt[i] = ++j;
else if (j > 0) j = nxt[j];
else nxt[i] = 0;
}
int i = 0, j = 0;
while (i < len1 && j < len2) {
if (s1[i] == s2[j]) i++, j++;
else if (j != 0) j = nxt[j];
else i++;
}
delete[] nxt;
return j == len2 ? i - len2 : -1;
}
int bf(char* s1, char* s2, int len1, int len2) {
for (int i = 0; i < len1; i++) {
bool b = 1;
for (int j = 0; j < len2; j++)
if (s1[j + i] != s2[j]) {
b = 0;
break;
}
if (b == 1) return i;
}
return -1;
}
int bm(char* s1, char* s2, int len1, int len2) {
// prebmbc
int bmbc[300];
for (int i = 0; i < 256; i++) bmbc[i] = len2;
for (int i = 0; i < len2 - 1; i++) bmbc[s2[i]] = len2 - 1 - i;
// prebmgs
int* suff = new int[len2 + 10];
int* bmgs = new int[len2 + 10];
suff[len2 - 1] = len2;
for (int i = len2 - 2; i >= 0; i--) {
int j = i;
while (j >= 0 && s2[j] == s2[len2 - 1 - i + j]) j--;
suff[i] = i - j;
}
for (int i = 0; i < len2; i++) bmgs[i] = len2;
for (int i = len2 - 1; i >= 0; i--)
if (suff[i] == i + 1)
for (int j=0 ; j < len2 - 1 ; j++)
if (bmgs[j] == len2) bmgs[j] = len2 - 1 - i;
for (int i = 0; i <= len2 - 2; i++)
bmgs[len2 - 1 - suff[i]] = len2 - 1 - i;
//compare
int j = 0;
while (j <= len1 - len2) {
int i = 0;
for (i = len2 - 1; i >= 0 && s2[i] == s1[i + j]; i--);
if (i < 0) {
delete[]bmgs;
delete[]suff;
return j;
}
else
j += max(bmbc[s1[i + j]] - len2 + 1 + i, bmgs[i]);
}
delete[]bmgs;
delete[]suff;
return -1;
}
string make_string(int len) {//构造数据函数
string s;
for (int i = 0; i < len; i++)
s.push_back(char('a' + rand() % 26));
return s;
}
/*
14 5
abbabcababacab
babac
*/
int main()
{
int m, n;
cin >> n >> m;
char* s1 = new char[n + 10];
char* s2 = new char[m + 10];
/*
//自动构造大数据进行时间测试
string s = make_string(n);
//cout << s << endl;
for (int i = 0; i < n; i++)
s1[i] = s[i];
for (int i = n-m-5,j=0; i < n-5; j++,i++)
s2[j] = s[i];
*/
//小数据判断正确性
for (int i = 0; i < n; i++)
cin >> s1[i];
for (int i = 0; i < m; i++)
cin >> s2[i];
clock_t start = clock();
cout<<"bf result:" << bf(s1, s2, n, m) << endl;
clock_t end = clock();
cout <<"bf time:" << (double)(end - start) / CLOCKS_PER_SEC * 1000 << "ms" << endl;
start = clock();
cout << "kmp result:" << kmp(s1, s2, n, m) << endl;
end = clock();
cout << "kmp time:" << (double)(end - start) / CLOCKS_PER_SEC * 1000 << "ms" << endl;
start = clock();
cout << "bm result:" << bm(s1, s2, n, m) << endl;
end = clock();
cout << "bm time:" << (double)(end - start) / CLOCKS_PER_SEC * 1000 << "ms" << endl;
delete[] s1;
delete[] s2;
return 0;
}