子字符串查找算法

刚写了几个字符串查找的算法，最朴素的字符串查找，RK算法，KMP算法。Java版实现如下：

public class FindSubString { //最朴素的字符串查找 public static int subString(String source, String subject){ int srcLen = source.length(); int subLen = subject.length(); for(int i=0; i<srcLen-subLen; i++){ int k = i; for(int j=0; j<subLen; j++,k++){ if(source.charAt(k)!=subject.charAt(j)) break; if(j == subLen-1) return i; } } return -1; } //借鉴Rabin-Karp算法(参见算法导论) public static int subStringRK(String source, String subject){ int srcLen = source.length(); int subLen = subject.length(); int value = 0; int sourceValue = 0; for(int i=0; i<subLen; i++){ value += subject.charAt(i); sourceValue += source.charAt(i); } int index = 0; while(index < (srcLen - subLen)){ while((sourceValue != value)&&(index < (srcLen - subLen))){ sourceValue = sourceValue - source.charAt(index) +source.charAt(index+subLen); index++; } for(int j=0,k=index; j<subLen; j++,k++){ if(source.charAt(k) != subject.charAt(j)){ index++; break; } if(j == (subLen -1)) return index; } } return -1; } //KMP算法(参见算法导论) public static int subStringKMP(String source, String subject){ int srcLen = source.length(); int subLen = subject.length(); int[] pattern = new int[subLen]; prefix(subject, pattern); for(int index=0,p=0; index<srcLen; index++){ if(source.charAt(index) == subject.charAt(p)){ p++; if(p == subLen) return index - subLen + 1; }else{ p = pattern[p]; } } return -1; } //跳转前缀函数 private static void prefix(String subject,int[] pattern){ // int[] p = {0,0,1,2,3,4,5,6,0,1}; // pattern = p; int subLen = subject.length(); pattern[0] = 0; for(int i=1,k=0; i<subLen; i++){ while ((subject.charAt(i) != subject.charAt(k)) && k > 0){ k = pattern[k]; } if(subject.charAt(i) == subject.charAt(k)){ k++; } pattern[i] = k; } // for(int p: pattern) // System.out.print(p); } public static void main(String[] args){ String source = "asgwebcdefghijkababababcalmn"; String subject = "ababababca"; System.out.println(subString(source,subject)); System.out.println(subStringRK(source,subject)); System.out.println(subStringKMP(source,subject)); } }