LeetCode 付费题目 247

Author: LjyYano

solution/0200-0299/0247.Strobogrammatic Number II/README.md

@@ -4,7 +4,15 @@
 
 ## 题目描述
 <!-- 这里写题目描述 -->
-None
+<p>中心对称数是指一个数字在旋转了&nbsp;180 度之后看起来依旧相同的数字（或者上下颠倒地看）。</p>
+
+<p>找到所有长度为 n 的中心对称数。</p>
+
+<p><strong>示例</strong> <strong>:</strong></p>
+
+<pre><strong>输入:</strong>  n = 2
+<strong>输出:</strong> <code>["11","69","88","96"]</code>
+</pre>
 
 
 ## 解法
@@ -32,4 +40,4 @@ None
 
 ```
 
-<!-- tabs:end -->
+<!-- tabs:end -->

solution/0200-0299/0247.Strobogrammatic Number II/README_EN.md

@@ -3,7 +3,15 @@
 [中文文档](/solution/0200-0299/0247.Strobogrammatic%20Number%20II/README.md)
 
 ## Description
-None
+<p>A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).</p>
+
+<p>Find all strobogrammatic numbers that are of length = n.</p>
+
+<p><b>Example:</b></p>
+
+<pre><b>Input:</b>  n = 2
+<b>Output:</b> <code>["11","69","88","96"]</code>
+</pre>
 
 
 ## Solutions
@@ -28,4 +36,4 @@ None
 
 ```
 
-<!-- tabs:end -->
+<!-- tabs:end -->

solution/0200-0299/0247.Strobogrammatic Number II/Solution.java

@@ -0,0 +1,51 @@
+class Solution {
+    Map<Character, Character> map = new HashMap<>();
+    {
+        map.put('1', '1');
+        map.put('0', '0');
+        map.put('6', '9');
+        map.put('9', '6');
+        map.put('8', '8');
+    }
+
+    public List<String> findStrobogrammatic(int n) {
+        if (n == 1) {
+            return Arrays.asList("0", "1", "8");
+        }
+        List<String> ans = new ArrayList<>();
+        dfs(n, ans, "");
+        return ans;
+    }
+
+    private void dfs(int n, List<String> ans, String tmp) {
+        if (tmp.length() == (n + 1) / 2) {
+            fillAns(n, ans, tmp);
+            return;
+        }
+
+        for (char c : map.keySet()) {
+            int num = c - '0';
+            // 首位不能是0
+            if (tmp.length() == 0 && num == 0) {
+                continue;
+            }
+            // 奇数的中间位只能是 0 1 8
+            if (n % 2 != 0 && tmp.length() == n / 2 && !(num == 0 || num == 1 || num == 8)) {
+                continue;
+            }
+            dfs(n, ans, tmp + num);
+        }
+    }
+
+    private void fillAns(int n, List<String> ans, String tmp) {
+        char[] a = new char[n];
+        for (int i = 0; i < tmp.length(); i++) {
+            a[i] = tmp.charAt(i);
+            a[n - i - 1] = map.get(tmp.charAt(i));
+        }
+        if (n % 2 != 0) {
+            a[tmp.length() - 1] = tmp.charAt(tmp.length() - 1);
+        }
+        ans.add(new String(a));
+    }
+}