Solve the "Test for palindromic permutations" problem

README.md

@@ -183,7 +183,7 @@ Hash Tables
 | Problem                                                                  | Test         | Implemented |
 |--------------------------------------------------------------------------|:------------:|:-----------:|
 | [Partition into anagrams][212]                                           | [tests][213] |      ✓      |
-| [Test for palindromic permutations][214]                                 | [tests][215] |             |
+| [Test for palindromic permutations][214]                                 | [tests][215] |      ✓      |
 | [Is an anonymous letter constructible?][216]                             | [tests][217] |             |
 | [Implement an ISBN cache][218]                                           | [tests][219] |             |
 | [Compute the LCA, optimizing for close ancestors][220]                   | [tests][221] |             |
@@ -617,8 +617,8 @@ Honors Class
 [211]: in_progress.md
 [212]: htables/anagram.go
 [213]: htables/anagram_test.go
-[214]: in_progress.md
-[215]: in_progress.md
+[214]: htables/palindrom.go
+[215]: htables/palindrom_test.go
 [216]: in_progress.md
 [217]: in_progress.md
 [218]: in_progress.md

htables/palindrom.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2015, Peter Mrekaj. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE.txt file.
+
+package htables
+
+// CanFormPalindrome returns true if s can represent a palindrome.
+// The time complexity is O(n) and O(c) additional space is needed, where
+// c is the number of distinct characters in the string s.
+func CanFormPalindrome(s string) bool {
+	if len(s) == 0 {
+		return true
+	}
+
+	f := make(map[rune]int)
+	for _, c := range s {
+		f[c]++
+	}
+
+	var odd int
+	for _, cnt := range f {
+		if cnt%2 != 0 {
+			if odd++; odd != 1 {
+				return false
+			}
+		}
+	}
+	return true
+}

htables/palindrom_test.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2015, Peter Mrekaj. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE.txt file.
+
+package htables
+
+import (
+	"math/rand"
+	"testing"
+
+	"github.com/mrekucci/epi/internal/epiutil"
+)
+
+func TestCanFormPalindrome(t *testing.T) {
+	for _, test := range []struct {
+		in   string
+		want bool
+	}{
+		{"", true},
+		{"ab", false},
+		{"aab", true},
+		{"aaab", false},
+		{"aaabccc", false},
+		{"aaabcc", false},
+		{"edified", true},
+		{"界☺世", false},
+		{"世世☺", true},
+	} {
+		if got := CanFormPalindrome(test.in); got != test.want {
+			t.Errorf("CanFormPalindrome(%q) = %t; want %t", test.in, got, test.want)
+		}
+	}
+}
+
+func benchCanFormPalindrome(b *testing.B, size int) {
+	b.StopTimer()
+	s := epiutil.RandStr(size, "abcdefghijklmnopqrstuvwxyz", rand.NewSource(int64(size)))
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		CanFormPalindrome(s)
+	}
+}
+
+func BenchmarkCanFormPalindrome1e2(b *testing.B) { benchCanFormPalindrome(b, 1e2) }
+func BenchmarkCanFormPalindrome1e4(b *testing.B) { benchCanFormPalindrome(b, 1e4) }
+func BenchmarkCanFormPalindrome1e6(b *testing.B) { benchCanFormPalindrome(b, 1e6) }