public class KMP {
private String pat;
private int[][] dfa;
//dfa方法
public KMP(String pat) {
this.pat = pat;
int M = pat.length();
int R = 256;
dfa = new int[R][M];
dfa[pat.charAt(0)][0] = 1;
for (int X = 0, j = 1; j < M; j++) {
for (int c = 0; c < R; c++) {
dfa[c][j] = dfa[c][X];
}
dfa[pat.charAt(j)][j] = j + 1;
X = dfa[pat.charAt(j)][X];
}
}
public int search(String txt) {
int i, j, N = txt.length(), M = pat.length();
for (i = 0, j = 0; i < N && j < M; i++) {
j = dfa[txt.charAt(i)][j];
}
if (j == M) {
return i - M;
} else {
return N;
}
}
public static void main(String[] args) {
// String pat = args[0];
String pat = "aacaa";
// String txt = args[1];
String txt = "aabrcdereaacaabced";
KMP kmp = new KMP(pat);
StdOut.println("text: " + txt);
int offset = kmp.search(txt);
StdOut.print("pattern: ");
for (int i = 0; i < offset; i++) {
StdOut.print(" ");
}
StdOut.println(pat);
}
//next数组方法
public static int Next(String ts, String ps) {
char[] t = ts.toCharArray();
char[] p = ps.toCharArray();
int i = 0; // 主串的位置
int j = 0; // 模式串的位置
int[] next = getNext(ps);
while (i < t.length && j < p.length) {
if (j == -1 || t[i] == p[j]) { // 当j为-1时,要移动的是i,当然j也要归0
i++;
j++;
} else {
// i不需要回溯了
j = next[j]; // j回到指定位置
}
}
if (j == p.length) {
return i - j;
} else {
return -1;
}
}
public static int[] getNext(String ps) {
char[] p = ps.toCharArray();
int[] next = new int[p.length];
next[0] = -1;
int j = 0;
int k = -1;
while (j < p.length - 1) {
if (k == -1 || p[j] == p[k]) {
if (p[++j] == p[++k]) { // 当两个字符相等时要跳过
next[j] = next[k];
} else {
next[j] = k;
}
} else {
k = next[k];
}
}
return next;
}
}
KMP算法之dfa与next数组
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转载自blog.csdn.net/abel004/article/details/84949289
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