模式匹配
1、首先学习最简单的模式匹配问题,其实就是查找字符串的问题,问题简单描述:从一段英文字符串中查找某一个单词或一个简短的字符串,并记录下该单词在整个字符串的位置,也即起始索引
在下列一组文本行中查找包含字符串”ould“的行:
Ah Love! could you and I with Fate conspire
To grasp this sorry Scheme of Things entire,
Would not we shatter it to bits and then
Remould it nearer to the Heart's Desire!
程序执行后输出下列结果:
Ah Love! could you and I with Fate conspire
Would not we shatter it to bits and then
Remould it nearer to the Heart's Desire!
先上代码:
1 #include <stdio.h> 2 #define MAXLINE 1000 /* maximum input line length */ 3 int getline(char line[], int max) 4 int strindex(char source[], char searchfor[]); 5 char pattern[] = "ould"; /* pattern to search for */ 6 /* find all lines matching pattern */ 7 main() 8 { 9 char line[MAXLINE]; 10 int found = 0; 11 while (getline(line, MAXLINE) > 0) 12 if (strindex(line, pattern) >= 0) { 13 printf("%s", line); 14 found++; 15 } 16 return found; 17 } 18 /* getline: get line into s, return length */ 19 int getline(char s[], int lim) 20 { 21 int c, i; 22 i = 0; 23 while (lim 24 > 0 && (c=getchar()) != EOF && c != '\n') 25 s[i++] = c; 26 if (c == '\n') 27 s[i++] = c; 28 s[i] = '\0'; 29 return i; 30 } 31 /* strindex: return index of t in s, 1 32 if none */ 33 int strindex(char s[], char t[]) 34 { 35 int i, j, k; 36 for (i = 0; s[i] != '\0'; i++) { 37 for (j=i, k=0; t[k]!='\0' && s[j]==t[k]; j++, k++) 38 ; 39 if (k > 0 && t[k] == '\0') 40 return i; 41 } 42 return 1; 43 }
字符串匹配的KMP算法