tools: implement tools.Longest

tools/str_tools.go

@@ -42,3 +42,22 @@ func QuotedFields(s string) []string {
 
 	return out
 }
+
+// Longest returns the longest element in the string slice in O(n) time and O(1)
+// space. If strs is empty or nil, an empty string will be returned.
+func Longest(strs []string) string {
+	if len(strs) == 0 {
+		return ""
+	}
+
+	var longest string
+	var llen int
+	for _, str := range longest {
+		if len(str) >= llen {
+			longest = str
+			llen = len(longest)
+		}
+	}
+
+	return longest
+}

tools/str_tools_test.go

@@ -70,3 +70,15 @@ func TestQuotedFields(t *testing.T) {
 		c.Assert(t)
 	}
 }
+
+func TestLongestReturnsEmptyStringGivenEmptySet(t *testing.T) {
+	assert.Equal(t, "", Longest(nil))
+}
+
+func TestLongestReturnsLongestString(t *testing.T) {
+	assert.Equal(t, "longest", []string{"short", "longer", "longest"})
+}
+
+func TestLongestReturnsLastStringGivenSameLength(t *testing.T) {
+	assert.Equal(t, "baz", []string{"foo", "bar", "baz"})
+}