Merge pull request #779 from vaskoz/day386

Day386

README.md

@@ -381,4 +381,5 @@ problems from
 * [Day 383](https://github.com/vaskoz/dailycodingproblem-go/issues/772)
 * [Day 384](https://github.com/vaskoz/dailycodingproblem-go/issues/776)
 * [Day 385](https://github.com/vaskoz/dailycodingproblem-go/issues/774)
+* [Day 386](https://github.com/vaskoz/dailycodingproblem-go/issues/778)
 

day386/problem.go

@@ -0,0 +1,28 @@
+package day386
+
+import "sort"
+
+// SortStringByCharFreq sorts the string by character
+// frequency with the most frequent letters first.
+// For a tie-breaker, they're sorted in reverse alphabetical
+// order.
+func SortStringByCharFreq(s string) string {
+	freq := make(map[rune]int)
+	runes := []rune(s)
+
+	for _, r := range runes {
+		freq[r]++
+	}
+
+	sort.Slice(runes, func(i, j int) bool {
+		if f1, f2 := freq[runes[i]], freq[runes[j]]; f1 > f2 {
+			return true
+		} else if f1 == f2 {
+			return runes[i] > runes[j]
+		}
+
+		return false
+	})
+
+	return string(runes)
+}

day386/problem_test.go

@@ -0,0 +1,29 @@
+package day386
+
+import "testing"
+
+// nolint
+var testcases = []struct {
+	input, expected string
+}{
+	{"tweet", "tteew"},
+	{"happiness", "ssppnihea"},
+}
+
+func TestSortStringByCharFreq(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if res := SortStringByCharFreq(tc.input); res != tc.expected {
+			t.Errorf("Expected %v, got %v", tc.expected, res)
+		}
+	}
+}
+
+func BenchmarkSortStringByCharFreq(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			SortStringByCharFreq(tc.input)
+		}
+	}
+}