KMP算法：
1 #include<iostream> 2 #include<string> 3 using namespace std; 4 5 /* 朴素的模式匹配法 */ 6 int Index(string s, string t, int pos) 7 { 8 int i = pos; 9 int j = 0; 10 int len_1 = s.size(); 11 int len_2 = t.size(); 12 while(i<len_1 && j<len_2) 13 { 14 if(s[i] == t[j]) 15 { 16 i++; 17 j++; 18 } 19 else 20 { 21 i = i-j+1; 22 j = 0; 23 } 24 } 25 if(j>=len_2) 26 return i-len_2; 27 else 28 return 0; 29 } 30 31 /* 通过计算返回子串T的next数组。 */ 32 void get_next(string T, int *next) 33 { 34 int len = T.size(); 35 int i = 0; 36 int j = -1; 37 next[0] = -1; 38 while(i<len-1) 39 { 40 if(j==-1 || T[i]==T[j]) 41 { 42 ++i; 43 ++j; 44 next[i] = j; 45 } 46 else 47 j = next[j]; 48 } 49 } 50 /* KMP算法 */ 51 int Index_KMP1(string s, string t, int pos) 52 { 53 int i = pos; 54 int j = 0; 55 int size1 = s.size(); 56 int size2 = t.size(); 57 //int *next = new int[size1]; 58 int next[255] = {0}; 59 get_next(t,next); 60 while(i<size1 && j<size2) 61 { 62 if(j==-1 || s[i]==t[j]) 63 { 64 i++; 65 j++; 66 } 67 else 68 { 69 j = next[j]; 70 } 71 } 72 if(j>=size2) 73 { 74 return i-size2; 75 } 76 else 77 return 0; 78 } 79 80 /* 求模式串T的next函数修正值并存入数组nextval */ 81 void get_nextval(string T, int *nextval) 82 { 83 int len = T.size(); 84 int i = 0; 85 int j = -1; 86 nextval[0] = -1; 87 while(i<len-1) 88 { 89 if(j==-1 || T[i]==T[j]) 90 { 91 ++i; 92 ++j; 93 if(T[i] != T[j]) 94 nextval[i] = j; 95 else 96 nextval[i] = nextval[j]; 97 } 98 else 99 j = nextval[j]; 100 } 101 } 102 103 /* 改进的KMP算法 */ 104 int Index_KMP2(string s, string t, int pos) 105 { 106 int i = pos; 107 int j = 0; 108 int size1 = s.size(); 109 int size2 = t.size(); 110 //int *next = new int[size1]; 111 int nextval[255] = {0}; 112 get_nextval(t,nextval); 113 while(i<size1 && j<size2) 114 { 115 if(j==-1 || s[i]==t[j]) 116 { 117 i++; 118 j++; 119 } 120 else 121 { 122 j = nextval[j]; 123 } 124 } 125 if(j>=size2) 126 { 127 return i-size2; 128 } 129 else 130 return 0; 131 } 132 133 int main() 134 { 135 //char str_2[6] = "abcde"; 136 //string str1 = "abcdex"; 137 //string str2 = "abcabx"; 138 //string str3 = "ababaaaba"; 139 string str4 = "aaaaaaaab"; 140 141 string s1 = "abaabcabx"; 142 string t1 = "abcabx"; 143 144 string s2 = "abcba"; 145 string t2 = "cba"; 146 147 cout<<Index(s2,t2,0)<<endl; 148 cout<<Index_KMP1(s2,t2,0)<<endl; 149 cout<<Index_KMP2(s2,t2,0)<<endl; 150 151 int arr1[255] = {0}; 152 int arr2[255] = {0}; 153 get_next(str4, arr1); 154 get_nextval(str4, arr2); 155 for(int i=0; i<str4.size(); i++) 156 cout<<arr1[i]; 157 for(int i=0; i<str4.size(); i++) 158 cout<<arr2[i]; 159 160 /*string aa = "12345"; 161 cout<<aa.size()<<endl; 162 for(int i=0;i<2;i++) 163 aa[i] = 'a'; 164 cout<<aa.size()<<endl; 165 cout<<aa<<endl;*/ 166 167 return 0; 168 }