add 2351

Author: luliyucoordinate

README.md

@@ -790,6 +790,7 @@ LeetCode
 |2225|[Find Players With Zero or One Losses](https://leetcode.com/problems/find-players-with-zero-or-one-losses/)||[c++](./src/2225-Find-Players-With-Zero-or-One-Losses/2225.cpp)||||||Medium|
 |2256|[Minimum Average Difference](https://leetcode.com/problems/minimum-average-difference/)||[c++](./src/2256-Minimum-Average-Difference/2256.cpp)||||||Medium|
 |2279|[Maximum Bags With Full Capacity of Rocks](https://leetcode.com/problems/maximum-bags-with-full-capacity-of-rocks/)||[c++](./src/2279-Maximum-Bags-With-Full-Capacity-of-Rocks/2279.cpp)||||||Medium|
+|2351|[First Letter to Appear Twice](https://leetcode.com/problems/first-letter-to-appear-twice/)||[c++](./src/2351-First-Letter-to-Appear-Twice/2351.cpp)||||||Easy|
 |2389|[Longest Subsequence With Limited Sum](https://leetcode.com/problems/longest-subsequence-with-limited-sum/)||[c++](./src/2389-Longest-Subsequence-With-Limited-Sum/2389.cpp)||||||Easy|
 |2469|[Convert the temperature](https://leetcode.com/problems/convert-the-temperature/)||[c++](./src/2469-Convert-the-Temperature/2469.cpp)||||||Easy|
 |2470|[Number of Subarrays With LCM Equal to K](https://leetcode.com/problems/number-of-subarrays-with-lcm-equal-to-k/)||[c++](./src/2470-Number-of-Subarrays-With-LCM-Equal-to-K/2470.cpp)||||||Medium|

src/2351-First-Letter-to-Appear-Twice/2351.cpp

@@ -0,0 +1,12 @@
+class Solution {
+ public:
+  char repeatedCharacter(string s) {
+    int cnt[26] = {};
+    for (auto c : s) {
+      auto x = c - 'a';
+      if (cnt[x]) return c;
+      cnt[x]++;
+    }
+    return ' ';
+  }
+};