计数排序

Author: tianqing.liang

21-Hash-Table/Solution.dart

@@ -9,10 +9,10 @@ class Solution {
 
     List freq = List.empty(growable: true);
     for(int i = 0 ; i < s.length ; i ++) {
-      freq[int.parse(s[i]) - int.parse('a')] ++;
+      freq[s[i].codeUnits[0] - 'a'.codeUnits[0]] ++;
     }
     for(int i = 0 ; i < s.length ; i ++) {
-      if (freq[int.parse(s[i]) - int.parse('a')] == 1) {
+      if (s[i].codeUnits[0] - 'a'.codeUnits[0] == 1) {
         return i;
       }
     }

22-CountingSort-And-RadixSort/Main.dart

@@ -0,0 +1,87 @@
+import 'Student.dart';
+import 'dart:math';
+
+void main() {
+  print("abcdefghijklmnopqrstuvwxyz".codeUnits);
+  print("abcdefghijklmnopqrstuvwxyz".runes);
+  print(String.fromCharCode("abcdefghijklmnopqrstuvwxyz".codeUnits[0]));
+  print(String.fromCharCode("abcdefghijklmnopqrstuvwxyz".codeUnits[0]));
+  Iterable<int>? string = [
+    97,
+    98,
+    99,
+    100,
+    101,
+    102,
+    103,
+    104,
+    105,
+    106,
+    107,
+    108,
+    109,
+    110,
+    111,
+    112,
+    113,
+    114,
+    115,
+    116,
+    117,
+    118,
+    119,
+    120,
+    121,
+    122
+  ];
+  print(String.fromCharCodes(string, 0, 26));
+
+  int n = 26 * 26 * 26 * 26;
+
+  List students = List.filled(n, Student, growable: true);
+  int k = 0;
+  Random rnd = new Random();
+  for (var c1 = 'a'.codeUnits[0]; c1 <= 'z'.codeUnits[0]; c1++)
+    for (var c2 = 'a'.codeUnits[0]; c2 <= 'z'.codeUnits[0]; c2++)
+      for (var c3 = 'a'.codeUnits[0]; c3 <= 'z'.codeUnits[0]; c3++)
+        for (var c4 = 'a'.codeUnits[0]; c4 <= 'z'.codeUnits[0]; c4++) {
+          students[k] = new Student(
+              "${String.fromCharCode(c1)} + ${String.fromCharCode(c2)} + ${String.fromCharCode(c3)} + ${String.fromCharCode(c4)}",
+              rnd.nextInt(101));
+          k++;
+        }
+
+  // 计数排序过程
+  int R = 101;
+
+  // O(n)
+  List cnt = List.filled(R, int, growable: true);
+  for (Student student in students) cnt[student.getScore()!]++;
+
+  // O(R)
+  List index = List.filled(R + 1, int, growable: true);
+  for (int i = 0; i < R; i++) index[i + 1] = index[i] + cnt[i];
+
+  // O(n)
+  List temp = List.filled(n, Student, growable: true);
+  for (Student student in students) {
+    temp[index[student.getScore()!]] = student;
+    index[student.getScore()!]++;
+  }
+
+  // O(n)
+  for (int i = 0; i < n; i++) students[i] = temp[i];
+
+  // O(n + R)
+
+  // 验证计数排序算法
+  for (int i = 1; i < n; i++) {
+    if (students[i - 1].getScore() > students[i].getScore())
+      throw new Exception("Sort failed");
+
+    if (students[i - 1].getScore() == students[i].getScore()) {
+      if (students[i - 1].getName().compareTo(students[i].getName()) >= 0)
+        throw new Exception("Non-Stable counting sort!");
+    }
+  }
+}

22-CountingSort-And-RadixSort/Solution.dart

@@ -0,0 +1,40 @@
+class Solution {
+  sortColors(List<int> nums) {
+    List? cnt = List.filled(3, int, growable: true);
+    for (int num in nums!) {
+      cnt[num]++;}
+
+    for (int i = 0; i < cnt[0]; i++) {
+      nums[i] = 0;
+    }
+    for (int i = cnt[0]; i < cnt[0] + cnt[1]; i++) {
+      nums[i] = 1;
+    }
+    for (int i = cnt[0] + cnt[1]; i < cnt[0] + cnt[1] + cnt[2]; i++) {
+      nums[i] = 2;
+    }
+  }
+
+  sortColors2(List<int> nums) {
+    // 处理元素取值范围是 [0, R) 的计数排序
+    int R = 3;
+
+    List? cnt = List.filled(3, int, growable: true);
+    for (int num in nums!) {
+      cnt[num]++;
+    }
+
+    // [index[i], index[i + 1]) 的值为 i
+    List? index = List.filled(R + 1, , int, growable: true);
+    for (int i = 0; i < R; i++) {
+      index[i + 1] = index[i] + cnt[i];
+    }
+
+    for (int i = 0; i + 1 < index.length; i++) {
+      // [index[i], index[i + 1]) 的值为 i
+      for (int j = index[i]; j < index[i + 1]; j++){
+        nums[j] = i;
+      }
+    }
+  }
+}

22-CountingSort-And-RadixSort/Student.dart

@@ -0,0 +1,25 @@
+class Student {
+
+  String? name;
+  int? score;
+
+  Student(this.name,this.score);
+
+  @override
+  num? compareTo(other) {
+    return  this.score! - other.score;
+  }
+
+  String? getName(){
+    return name;
+  }
+
+  int? getScore(){
+    return score;
+  }
+
+  @override
+  toString(){
+    return "Student(name: $name, score: $score)";
+  }
+}

README.md

@@ -1,7 +1,8 @@
 # AlgorithmAndDataArchitecture
 
-#### 介绍
-使用Dart语言编写 [慕课网算法与数据结构](https://class.imooc.com/sale/datastructure)
+## 介绍
+<h2>使用Dart语言重写数据结构与算法</h2>
+
 1. 线性搜索
 2. 选择排序
 3. 插入排序
@@ -23,6 +24,8 @@
 19. AVL树
 20. 红黑树
 21. 哈希表
+22. 计数排序
 
 #### SDK版本
 1. 版本：2.12.3
+2. Java版本课程地址：[慕课网算法与数据结构](https://class.imooc.com/sale/datastructure)