Add kmp

Author: willzhen

kmp.go

@@ -0,0 +1,72 @@
+package textalg
+
+// Kmp 快速字符串匹配算法，时间复杂度 O(n + m), 其中 n 代表模式串的长度，m 代码匹配母串的长度
+type Kmp struct {
+	pattern string
+	next    []int
+}
+
+// BuildKmp 构建 kmp
+// patternStr 模式串
+func BuildKmp(patternStr string) *Kmp {
+	kmp := Kmp{
+		pattern: patternStr,
+	}
+	kmp.buildNext(0)
+	return &kmp
+}
+
+func (k *Kmp) buildNext(start int) {
+	r := []rune(k.pattern)
+	l := len(r)
+	// next 要多构建 1 个长度
+	for i := start; i <= l; i++ {
+		if i == 0 || i == 1 {
+			k.next = append(k.next, 0) // next[0] and next[1] is 0
+			continue
+		}
+		j := k.next[i-1]
+		for ; j > 0 && r[i-1] != r[j]; j = k.next[j] {
+		}
+		if r[i-1] == r[j] {
+			j++
+		}
+		k.next = append(k.next, j)
+	}
+}
+
+// AppendPatternStr 扩充模式串长度
+func (k *Kmp) AppendPatternStr(patternStr string) {
+	start := len([]rune(k.pattern)) + 1
+	k.pattern += patternStr
+	k.buildNext(start)
+}
+
+// ResetPatternStr 重置模式串
+func (k *Kmp) ResetPatternStr(patternStr string) {
+	k.pattern = patternStr
+	k.next = nil
+	k.buildNext(0)
+}
+
+// Search 返回所有 pattern 在 content 中出现的开始位置的 index
+func (k Kmp) Search(content string) (indexs []int) {
+	rpattern, rcontent := []rune(k.pattern), []rune(content)
+	n, m := len(rcontent), len(rpattern)
+	if n == 0 || m == 0 {
+		return nil
+	}
+	j := 0
+	for i := 0; i < n; i++ {
+		for ; j > 0 && rcontent[i] != rpattern[j]; j = k.next[j] {
+		}
+		if rcontent[i] == rpattern[j] {
+			j++
+		}
+		if j == m {
+			indexs = append(indexs, i-m+1)
+			j = k.next[j]
+		}
+	}
+	return indexs
+}

text_test.go

@@ -33,3 +33,24 @@ func TestSliceSmae(t *testing.T) {
 	// test can not change order of a
 	t.Log(a)
 }
+
+func TestKmp(t *testing.T) {
+	k := textalg.BuildKmp("a")
+	indexs := k.Search("aaaaab") // find "a" in "aaaaab"
+	t.Log(indexs)
+	k.AppendPatternStr("a")
+	indexs = k.Search("aaaaab") // find "aa" in "aaaaab"
+	t.Log(indexs)
+	k.AppendPatternStr("a")
+	indexs = k.Search("aaaaab") // find "aaa" in "aaaaab"
+	t.Log(indexs)
+	k.AppendPatternStr("b")
+	indexs = k.Search("aaaaab") // find "aaab" in "aaaaab"
+	t.Log(indexs)
+	k.AppendPatternStr("b")
+	indexs = k.Search("aaaaab") // find "aaabb" in "aaaaab"
+	t.Log(indexs)
+	k.ResetPatternStr("ab")
+	indexs = k.Search("aaaaab") // find "ab" in "aaaaab"
+	t.Log(indexs)
+}