Add solved exercises

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diff --git a/go/hamming/README.md b/go/hamming/README.md
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+# Hamming
+
+Calculate the Hamming Distance between two DNA strands.
+
+Your body is made up of cells that contain DNA. Those cells regularly wear out and need replacing, which they achieve by dividing into daughter cells. In fact, the average human body experiences about 10 quadrillion cell divisions in a lifetime!
+
+When cells divide, their DNA replicates too. Sometimes during this process mistakes happen and single pieces of DNA get encoded with the incorrect information. If we compare two strands of DNA and count the differences between them we can see how many mistakes occurred. This is known as the "Hamming Distance".
+
+We read DNA using the letters C,A,G and T. Two strands might look like this:
+
+    GAGCCTACTAACGGGAT
+    CATCGTAATGACGGCCT
+    ^ ^ ^  ^ ^    ^^
+
+They have 7 differences, and therefore the Hamming Distance is 7.
+
+The Hamming Distance is useful for lots of things in science, not just biology, so it's a nice phrase to be familiar with :)
+
+# Implementation notes
+
+The Hamming distance is only defined for sequences of equal length, so
+an attempt to calculate it between sequences of different lengths should
+not work. The general handling of this situation (e.g., raising an
+exception vs returning a special value) may differ between languages.
+
+You may be wondering about the `cases_test.go` file. We explain it in the
+[leap exercise][leap-exercise-readme].
+
+[leap-exercise-readme]: https://github.com/exercism/go/blob/master/exercises/leap/README.md 
+
+
+## Coding the solution
+
+Look for a stub file having the name hamming.go
+and place your solution code in that file.
+
+## Running the tests
+
+To run the tests run the command `go test` from within the exercise directory.
+
+If the test suite contains benchmarks, you can run these with the `--bench` and `--benchmem`
+flags:
+
+    go test -v --bench . --benchmem
+
+Keep in mind that each reviewer will run benchmarks on a different machine, with
+different specs, so the results from these benchmark tests may vary.
+
+## Further information
+
+For more detailed information about the Go track, including how to get help if
+you're having trouble, please visit the exercism.io [Go language page](http://exercism.io/languages/go/resources).
+
+## Source
+
+The Calculating Point Mutations problem at Rosalind [http://rosalind.info/problems/hamm/](http://rosalind.info/problems/hamm/)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
diff --git a/go/hamming/cases_test.go b/go/hamming/cases_test.go
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+package hamming
+
+// Source: exercism/problem-specifications
+// Commit: 4119671 Hamming: Add a tests to avoid wrong recursion solution (#1450)
+// Problem Specifications Version: 2.3.0
+
+var testCases = []struct {
+	s1          string
+	s2          string
+	want        int
+	expectError bool
+}{
+	{ // empty strands
+		"",
+		"",
+		0,
+		false,
+	},
+	{ // single letter identical strands
+		"A",
+		"A",
+		0,
+		false,
+	},
+	{ // single letter different strands
+		"G",
+		"T",
+		1,
+		false,
+	},
+	{ // long identical strands
+		"GGACTGAAATCTG",
+		"GGACTGAAATCTG",
+		0,
+		false,
+	},
+	{ // long different strands
+		"GGACGGATTCTG",
+		"AGGACGGATTCT",
+		9,
+		false,
+	},
+	{ // disallow first strand longer
+		"AATG",
+		"AAA",
+		0,
+		true,
+	},
+	{ // disallow second strand longer
+		"ATA",
+		"AGTG",
+		0,
+		true,
+	},
+	{ // disallow left empty strand
+		"",
+		"G",
+		0,
+		true,
+	},
+	{ // disallow right empty strand
+		"G",
+		"",
+		0,
+		true,
+	},
+}
diff --git a/go/hamming/go.mod b/go/hamming/go.mod
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+module hamming
+
+go 1.13
diff --git a/go/hamming/hamming.go b/go/hamming/hamming.go
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+// hamming implements Distance.
+package hamming
+
+import "errors"
+
+// Distance returns the distance between 2 equal DNA strands.
+func Distance(strand1, strand2 string) (int, error) {
+	var dist int
+	if len(strand1) != len(strand2) {
+		return dist, errors.New("length not equal")
+	}
+	for idx := 0; idx < len(strand1); idx++ {
+		if strand1[idx] != strand2[idx] {
+			dist++
+		}
+	}
+	return dist, nil
+}
diff --git a/go/hamming/hamming_test.go b/go/hamming/hamming_test.go
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+package hamming
+
+import "testing"
+
+func TestHamming(t *testing.T) {
+	for _, tc := range testCases {
+		got, err := Distance(tc.s1, tc.s2)
+		if tc.expectError {
+			// check if err is of error type
+			var _ error = err
+
+			// we expect error
+			if err == nil {
+				t.Fatalf("Distance(%q, %q); expected error, got nil.",
+					tc.s1, tc.s2)
+			}
+		} else {
+			// we do not expect error
+			if err != nil {
+				t.Fatalf("Distance(%q, %q) returned unexpected error: %v",
+					tc.s1, tc.s2, err)
+			}
+			if got != tc.want {
+				t.Fatalf("Distance(%q, %q) = %d, want %d.",
+					tc.s1, tc.s2, got, tc.want)
+			}
+
+		}
+	}
+}
+
+func BenchmarkHamming(b *testing.B) {
+	// bench combined time to run through all test cases
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testCases {
+			// ignoring errors and results because we're just timing function execution
+			_, _ = Distance(tc.s1, tc.s2)
+		}
+	}
+}