28. Implement strStr()

Author: vfedorovatlas

implement_strstr/main.go

@@ -0,0 +1,37 @@
+package leecode
+
+const base = 16777619
+
+func hash(s string) uint32 {
+	var h uint32
+	for i := 0; i < len(s); i++ {
+		h = (h*base + uint32(s[i]))
+	}
+	return h
+}
+
+func strStr(haystack string, needle string) int {
+	n := len(haystack) // string len
+	m := len(needle)   // pattern len
+	switch {
+	case m == 0:
+		return m
+	case n == m:
+		if haystack == needle {
+			return 0
+		}
+		return -1
+	case m > n:
+		return -1
+	}
+	pattern := hash(needle)
+
+	for i := 0; i < (n-m)+1; i++ {
+		substr := haystack[i : i+m]
+		hs := hash(substr)
+		if hs == pattern {
+			return i
+		}
+	}
+	return -1
+}

implement_strstr/main_test.go

@@ -0,0 +1,40 @@
+package leecode
+
+import (
+	"fmt"
+	"testing"
+)
+
+var testCases = []struct {
+	Haystack string
+	Needle   string
+	Output   int
+}{
+	{
+		Haystack: "hello",
+		Needle:   "ll",
+		Output:   2,
+	},
+}
+
+func TestStrStr(t *testing.T) {
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("%s %s %d", tc.Haystack, tc.Needle, tc.Output), func(t *testing.T) {
+			actual := strStr(tc.Haystack, tc.Needle)
+			if actual != tc.Output {
+				t.Errorf("expects: %d gets: %d", tc.Output, actual)
+			}
+		})
+	}
+}
+
+func BenchmarkStrStr(b *testing.B) {
+	for _, tc := range testCases {
+		// run the Fib function b.N times
+		b.Run(fmt.Sprintf("%s %s %d", tc.Haystack, tc.Needle, tc.Output), func(b *testing.B) {
+			for n := 0; n < b.N; n++ {
+				strStr(tc.Haystack, tc.Needle)
+			}
+		})
+	}
+}