From 7e939c7cc9dc6a218193f794fdc8be7ca3f9ccb6 Mon Sep 17 00:00:00 2001
From: Mars Liu <mars.liu@outlook.com>
Date: Thu, 25 Nov 2021 01:20:41 +0800
Subject: [PATCH] add permutation

---
 .../5.\345\207\275\346\225\260/config.json"   |   3 +-
 .../permutation.json"                         |   7 +
 .../permutation.md"                           | 205 ++++++++++++++++++
 3 files changed, 214 insertions(+), 1 deletion(-)
 create mode 100644 "data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.json"
 create mode 100644 "data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.md"

diff --git "a/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/config.json" "b/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/config.json"
index 619ab8a..7faf1d7 100644
--- "a/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/config.json"
+++ "b/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/config.json"
@@ -7,6 +7,7 @@
   "children": [],
   "export": [
     "call.json",
-    "parser.json"
+    "parser.json",
+    "permutation.json"
   ]
 }
\ No newline at end of file
diff --git "a/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.json" "b/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.json"
new file mode 100644
index 0000000..040ed99
--- /dev/null
+++ "b/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.json"
@@ -0,0 +1,7 @@
+{
+  "type": "code_options",
+  "author": "刘鑫",
+  "source": "permutation.md",
+  "notebook_enable": false,
+  "exercise_id": "a52d29ac72cf48669824894ba7f7427a"
+}
\ No newline at end of file
diff --git "a/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.md" "b/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.md"
new file mode 100644
index 0000000..33c4494
--- /dev/null
+++ "b/data/1.Java\345\210\235\351\230\266/9.\346\216\247\345\210\266\346\211\247\350\241\214\346\265\201\347\250\213/5.\345\207\275\346\225\260/permutation.md"
@@ -0,0 +1,205 @@
+# 排列
+
+给定一个几十个字符内的短字符串，简单起见我们假设这个字符串没有重复字符，那么生成其全排列的代码是：
+
+## 答案
+
+```java
+package net.csdn;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Main {
+
+    public static String drop(String token, int idx){
+        if(idx==0){
+            return token.substring(1);
+        }
+        if(idx>=token.length()-1){
+            return token.substring(0, idx);
+        }
+        return token.substring(0, idx) + token.substring(idx+1);
+    }
+
+    public static List<String> permutation(String token){
+        if(token.length() < 2){
+            return List.of(token);
+        }
+        if(token.length()==2){
+            String item = token.charAt(1) + String.valueOf(token.charAt(0));
+            return List.of(token, item);
+        }
+        List<String> result = new ArrayList<>();
+        for(int idx=0;idx<token.length();idx++){
+            char chr = token.charAt(idx);
+            String next = drop(token, idx);
+
+            for(var rest: permutation(next)){
+                result.add(chr +rest);
+            }
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        String token = args[0];
+        for(var item: permutation(token)){
+            System.out.println(item);
+        }
+    }
+}
+```
+
+## 选项
+
+### 方法定义不对
+
+```java
+package net.csdn;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Main {
+
+    public String drop(String token, int idx) {
+        if (idx == 0) {
+            return token.substring(1);
+        }
+        if (idx >= token.length() - 1) {
+            return token.substring(0, idx);
+        }
+        return token.substring(0, idx) + token.substring(idx + 1);
+    }
+
+    public List<String> permutation(String token) {
+        if (token.length() < 2) {
+            return List.of(token);
+        }
+        if (token.length() == 2) {
+            String item = token.charAt(1) + String.valueOf(token.charAt(0));
+            return List.of(token, item);
+        }
+        List<String> result = new ArrayList<>();
+        for (int idx = 0; idx < token.length(); idx++) {
+            char chr = token.charAt(idx);
+            String next = drop(token, idx);
+
+            for (var rest : permutation(next)) {
+                result.add(chr + rest);
+            }
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        String token = args[0];
+        for (var item : permutation(token)) {
+            System.out.println(item);
+        }
+    }
+}
+```
+
+### 方法引用不对
+
+```java
+package net.csdn;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Main {
+
+    public static String drop(String token, int idx){
+        if(idx==0){
+            return token.substring(1);
+        }
+        if(idx>=token.length()-1){
+            return token.substring(0, idx);
+        }
+        return token.substring(0, idx) + token.substring(idx+1);
+    }
+
+    public static List<String> permutation(String token){
+        if(token.length() < 2){
+            return List.of(token);
+        }
+        if(token.length()==2){
+            String item = token.charAt(1) + String.valueOf(token.charAt(0));
+            return List.of(token, item);
+        }
+        List<String> result = new ArrayList<>();
+        for(int idx=0;idx<token.length();idx++){
+            char chr = token.charAt(idx);
+            String next = drop(token, idx);
+
+            for(var rest: permutation(next)){
+                result.add(chr +rest);
+            }
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        String token = args[0];
+        for(var item: this.permutation(token)){
+            System.out.println(item);
+        }
+    }
+}
+```
+
+### 方法定义不对
+
+```java
+package net.csdn;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Main {
+
+    String drop(String token, int idx){
+        if(idx==0){
+            return token.substring(1);
+        }
+        if(idx>=token.length()-1){
+            return token.substring(0, idx);
+        }
+        return token.substring(0, idx) + token.substring(idx+1);
+    }
+
+    List<String> permutation(String token){
+        if(token.length() < 2){
+            return List.of(token);
+        }
+        if(token.length()==2){
+            String item = token.charAt(1) + String.valueOf(token.charAt(0));
+            return List.of(token, item);
+        }
+        List<String> result = new ArrayList<>();
+        for(int idx=0;idx<token.length();idx++){
+            char chr = token.charAt(idx);
+            String next = drop(token, idx);
+
+            for(var rest: permutation(next)){
+                result.add(chr +rest);
+            }
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        String token = args[0];
+        for(var item: permutation(token)){
+            System.out.println(item);
+        }
+    }
+}
+```
+
+### D
+
+全都是错的，Java 函数不能递归调用
\ No newline at end of file
-- 
GitLab