Merge pull request #17 from SharingSource/ac_oier

✨feat: Add 483、1239

Author: SharingSource

Index/DFS.md

@@ -15,6 +15,7 @@
 | [872. 叶子相似的树](https://leetcode-cn.com/problems/leaf-similar-trees/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/leaf-similar-trees/solution/gong-shui-san-xie-yi-ti-shuang-jie-di-gu-udfc/) | 简单 | 🤩🤩🤩      |
 | [938. 二叉搜索树的范围和](https://leetcode-cn.com/problems/range-sum-of-bst/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/range-sum-of-bst/solution/gong-shui-san-xie-yi-ti-shuang-jie-di-gu-q2fo/) | 简单 | 🤩🤩🤩      |
 | [993. 二叉树的堂兄弟节点](https://leetcode-cn.com/problems/cousins-in-binary-tree/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/cousins-in-binary-tree/solution/gong-shui-san-xie-shu-de-sou-suo-dfs-bfs-b200/) | 简单 | 🤩🤩       |
+| [1239. 串联字符串的最大长度](https://leetcode-cn.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/solution/gong-shui-san-xie-yi-ti-san-jie-jian-zhi-nfeb/) | 中等 | 🤩🤩🤩      |
 | [1723. 完成所有工作的最短时间](https://leetcode-cn.com/problems/find-minimum-time-to-finish-all-jobs/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/find-minimum-time-to-finish-all-jobs/solution/gong-shui-san-xie-yi-ti-shuang-jie-jian-4epdd/) | 困难 | 🤩🤩🤩      |
 | [1766. 互质树](https://leetcode-cn.com/problems/tree-of-coprimes/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/tree-of-coprimes/solution/bu-tai-yi-yang-de-dfs-ji-lu-suo-you-zui-d3xeu/) | 困难 | 🤩🤩🤩🤩     |
 

Index/二进制枚举.md

@@ -0,0 +1,4 @@
+| 题目                                                         | 题解                                                         | 难度 | 推荐指数 |
+| ------------------------------------------------------------ | ------------------------------------------------------------ | ---- | -------- |
+| [1239. 串联字符串的最大长度](https://leetcode-cn.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/solution/gong-shui-san-xie-yi-ti-san-jie-jian-zhi-nfeb/) | 中等 | 🤩🤩🤩      |
+

Index/启发式搜索.md

@@ -1,4 +1,5 @@
 | 题目                                                         | 题解                                                         | 难度 | 推荐指数 |
 | ------------------------------------------------------------ | ------------------------------------------------------------ | ---- | -------- |
+| [1239. 串联字符串的最大长度](https://leetcode-cn.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/solution/gong-shui-san-xie-yi-ti-san-jie-jian-zhi-nfeb/) | 中等 | 🤩🤩🤩🤩🤩    |
 | [1723. 完成所有工作的最短时间](https://leetcode-cn.com/problems/find-minimum-time-to-finish-all-jobs/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/find-minimum-time-to-finish-all-jobs/solution/gong-shui-san-xie-yi-ti-shuang-jie-jian-4epdd/) | 困难 | 🤩🤩🤩🤩     |
 

Index/数学.md

@@ -12,6 +12,7 @@
 | [263. 丑数](https://leetcode-cn.com/problems/ugly-number/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/ugly-number/solution/gong-shui-san-xie-jian-dan-de-fen-qing-k-dlvg/) | 简单 | 🤩🤩 |
 | [342. 4的幂](https://leetcode-cn.com/problems/power-of-four/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/power-of-four/solution/gong-shui-san-xie-zhuan-hua-wei-2-de-mi-y21lq/) | 简单 | 🤩🤩🤩 |
 | [477. 汉明距离总和](https://leetcode-cn.com/problems/total-hamming-distance/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/total-hamming-distance/solution/gong-shui-san-xie-ying-yong-cheng-fa-yua-g21t/) | 简单 | 🤩🤩🤩 |
+| [483. 最小好进制](https://leetcode-cn.com/problems/smallest-good-base/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/smallest-good-base/solution/gong-shui-san-xie-xiang-jie-ru-he-fen-xi-r94g/) | 困难 | 🤩🤩🤩🤩 |
 | [523. 连续的子数组和](https://leetcode-cn.com/problems/continuous-subarray-sum/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/continuous-subarray-sum/solution/gong-shui-san-xie-tuo-zhan-wei-qiu-fang-1juse/) | 中等 | 🤩🤩🤩🤩 |
 | [633. 平方数之和](https://leetcode-cn.com/problems/sum-of-square-numbers/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/sum-of-square-numbers/solution/gong-shui-san-xie-yi-ti-san-jie-mei-ju-s-7qi5/) | 简单 | 🤩🤩 |
 | [810. 黑板异或游戏](https://leetcode-cn.com/problems/chalkboard-xor-game/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/chalkboard-xor-game/solution/gong-shui-san-xie-noxiang-xin-ke-xue-xi-ges7k/) | 困难 | 🤩🤩🤩🤩 |

LeetCode/121-130/127. 单词接龙（困难）.md

@@ -68,7 +68,7 @@ Tag : 「双向 BFS」
 
 **随着层数的加深，这个数字的增速越快，这就是「搜索空间爆炸」问题。**
 
-![](https://pic.leetcode-cn.com/1623894968-XELIvK-image.png)
+![image.png](https://pic.leetcode-cn.com/1623894968-XELIvK-image.png)
 
 **在朴素的 BFS 实现中，空间的瓶颈主要取决于搜索空间中的最大宽度。**
 
@@ -78,7 +78,7 @@ Tag : 「双向 BFS」
 
 **同时从两个方向开始搜索，一旦搜索到相同的值，意味着找到了一条联通起点和终点的最短路径。**
 
-![](https://pic.leetcode-cn.com/1623894976-CCMljJ-image.png)
+![image.png](https://pic.leetcode-cn.com/1623894976-CCMljJ-image.png)
 
 「双向 BFS」的基本实现思路如下：
 
@@ -212,6 +212,79 @@ class Solution {
 
 ---
 
+### 【补充】启发式搜索 AStar
+
+可以直接根据本题规则来设计 A* 的「启发式函数」。
+
+比如对于两个字符串 `a` `b` 直接使用它们不同字符的数量来充当估值距离，我觉得是合适的。
+
+因为不同字符数量的差值可以确保不会超过真实距离（是一个理论最小替换次数）。
+
+注意：本题数据比较弱，用 A* 过了，但通常我们需要「确保有解」，A* 的启发搜索才会发挥真正价值。而本题，除非 `endWord` 本身就不在 `wordList` 中，其余情况我们无法很好提前判断「是否有解」。这时候 A* 将不能带来「搜索空间的优化」，效果不如「双向 BFS」。
+
+代码：
+```Java []
+class Solution {
+    class Node {
+        String str;
+        int val;
+        Node (String _str, int _val) {
+            str = _str;
+            val = _val;
+        }
+    }
+    String s, e;
+    int INF = 0x3f3f3f3f;
+    Set<String> set = new HashSet<>();
+    public int ladderLength(String _s, String _e, List<String> ws) {
+        s = _s;
+        e = _e;
+        for (String w : ws) set.add(w);
+        if (!set.contains(e)) return 0;
+        int ans = astar();
+        return ans == -1 ? 0 : ans + 1;
+    }
+    int astar() {
+        PriorityQueue<Node> q = new PriorityQueue<>((a,b)->a.val-b.val);
+        Map<String, Integer> dist = new HashMap<>();
+        dist.put(s, 0);
+        q.add(new Node(s, f(s)));
+        
+        while (!q.isEmpty()) {
+            Node poll = q.poll();
+            String str = poll.str;
+            int distance = dist.get(str);
+            if (str.equals(e)) {
+                break;
+            }
+            int n = str.length();
+            for (int i = 0; i < n; i++) {
+                for (int j = 0; j < 26; j++) {
+                    String sub = str.substring(0, i) + String.valueOf((char)('a' + j)) + str.substring(i + 1);
+                    if (!set.contains(sub)) continue;
+                    if (!dist.containsKey(sub) || dist.get(sub) > distance + 1) {
+                        dist.put(sub, distance + 1);
+                        q.add(new Node(sub, dist.get(sub) + f(sub)));
+                    }
+                }
+            }
+        }
+        return dist.containsKey(e) ? dist.get(e) : -1;
+    }
+    int f(String str) {
+        if (str.length() != e.length()) return INF;
+        int n = str.length();
+        int ans = 0;
+        for (int i = 0; i < n; i++) {
+            ans += str.charAt(i) == e.charAt(i) ? 0 : 1;
+        }
+        return ans;
+    }
+}
+```
+
+---
+
 ### 最后
 
 这是我们「刷穿 LeetCode」系列文章的第 `No.127` 篇，系列开始于 2021/01/01，截止于起始日 LeetCode 上共有 1916 道题目，部分是有锁题，我们将先将所有不带锁的题目刷完。