添加 problem 451

Algorithms/0451. Sort Characters By Frequency/451. Sort Characters By Frequency.go

@@ -0,0 +1,35 @@
+package leetcode
+
+import (
+	"sort"
+)
+
+func frequencySort(s string) string {
+	if s == "" {
+		return ""
+	}
+	sMap := map[byte]int{}
+	cMap := map[int][]byte{}
+	sb := []byte(s)
+	for _, b := range sb {
+		sMap[b]++
+	}
+	for key, value := range sMap {
+		cMap[value] = append(cMap[value], key)
+	}
+
+	var keys []int
+	for k := range cMap {
+		keys = append(keys, k)
+	}
+	sort.Sort(sort.Reverse(sort.IntSlice(keys)))
+	res := make([]byte, 0)
+	for _, k := range keys {
+		for i := 0; i < len(cMap[k]); i++ {
+			for j := 0; j < k; j++ {
+				res = append(res, cMap[k][i])
+			}
+		}
+	}
+	return string(res)
+}

Algorithms/0451. Sort Characters By Frequency/451. Sort Characters By Frequency_test.go

@@ -0,0 +1,51 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question451 struct {
+	para451
+	ans451
+}
+
+// para 是参数
+// one 代表第一个参数
+type para451 struct {
+	one string
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans451 struct {
+	one string
+}
+
+func Test_Problem451(t *testing.T) {
+
+	qs := []question451{
+		question451{
+			para451{"tree"},
+			ans451{"eert"},
+		},
+
+		question451{
+			para451{"cccaaa"},
+			ans451{"cccaaa"},
+		},
+
+		question451{
+			para451{"Aabb"},
+			ans451{"bbAa"},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 451------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans451, q.para451
+		fmt.Printf("【input】:%v       【output】:%v\n", p, frequencySort(p.one))
+	}
+	fmt.Printf("\n\n\n")
+}

Algorithms/0451. Sort Characters By Frequency/README.md

@@ -0,0 +1,64 @@
+# [451. Sort Characters By Frequency](https://leetcode.com/problems/sort-characters-by-frequency/)
+
+## 题目
+
+Given a string, sort it in decreasing order based on the frequency of characters.
+
+
+Example 1:
+
+```c
+Input:
+"tree"
+
+Output:
+"eert"
+
+Explanation:
+'e' appears twice while 'r' and 't' both appear once.
+So 'e' must appear before both 'r' and 't'. Therefore "eetr" is also a valid answer.
+```
+
+Example 2:
+
+```c
+Input:
+"cccaaa"
+
+Output:
+"cccaaa"
+
+Explanation:
+Both 'c' and 'a' appear three times, so "aaaccc" is also a valid answer.
+Note that "cacaca" is incorrect, as the same characters must be together.
+```
+
+Example 3:
+
+```c
+Input:
+"Aabb"
+
+Output:
+"bbAa"
+
+Explanation:
+"bbaA" is also a valid answer, but "Aabb" is incorrect.
+Note that 'A' and 'a' are treated as two different characters.
+```
+
+
+
+
+## 题目大意
+
+这道题是 Google 的面试题。
+
+给定一个字符串，要求根据字符出现的频次从高到低重新排列这个字符串。
+
+## 解题思路
+
+思路比较简单，首先统计每个字符的频次，然后排序，最后按照频次从高到低进行输出即可。
+
+
+