【数据结构】KMP算法（c语言）

#include <stdio.h>
#include <string.h> 
#include <stdlib.h>
 
typedef int Position;	//返回数组下标
#define NotFound -1		
 
void BuildMatch( char *pattern, int *match )
{
    Position i, j;
    int m = strlen(pattern);
    match[0] = -1;				//match[0]肯定是-1
     
    for ( j=1; j<m; j++ ) {		//对每一个下标计算match值
        i = match[j-1];			//把前一个match值记在i里
        while ( (i>=0) && (pattern[i+1]!=pattern[j]) )
            i = match[i];		//让i回退
        if ( pattern[i+1]==pattern[j] )
             match[j] = i+1;
        else match[j] = -1;
    }
}
 
Position KMP( char *string, char *pattern )
{
    int n = strlen(string);		//得到字符串长度
    int m = strlen(pattern);	//得到模式串长度
    Position s, p, *match;
     
    if ( n < m ) return NotFound;
    match = (Position *)malloc(sizeof(Position) * m);	//定义整型数组match
    BuildMatch(pattern, match);			//计算match的值
    s = p = 0;							//一开始指向起点0
    while ( s<n && p<m ) {				//s和p都还没到结尾
        if ( string[s]==pattern[p] ) {
            s++; p++;					//相配则一起往前移动
        }
        else if (p>0) p = match[p-1]+1;	//不相配，p指针往回移
        else s++;						//p=0，第一个字符就不匹配，s指针往前移
    }
    return ( p==m )? (s-m) : NotFound;	//p到结尾，匹配成功，返回匹配上的位置s-m。否则匹配失败
}
 
int main()
{
    char string[] = "This is a simple example.";
    char pattern[] = "simple";
    Position p = KMP(string, pattern);
    if (p==NotFound) printf("Not Found.\n");
    else printf("%s\n", string+p);
    return 0;  
}

代码来自中国大学MOOC浙江大学版数据结构