format filename

Author: HONGJICAI

README.md

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+class Solution {
+public:
+  vector<int> twoSum(vector<int> &nums, int target) {
+    unordered_map<int, int> map;
+    for (int i = 0; i < nums.size(); ++i) {
+      if (auto it = map.find(target - nums[i]); it != map.end())
+        return {it->second, i};
+      map[nums[i]] = i;
+    }
+    return {};
+  }
+};

cpp/1.TwoSum.cpp

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+// recursion-3ms.cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+  bool isSameTree(TreeNode *p, TreeNode *q) {
+    if (p == NULL || q == NULL)
+      return p == q;
+    return p->val == q->val && isSameTree(p->left, q->left) &&
+           isSameTree(p->right, q->right);
+  }
+};

cpp/1.cpp

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+class Solution { // 8ms  99.37%
+public:
+  vector<string> commonChars(vector<string> &A) {
+    vector<int> arr(26, numeric_limits<int>::max());
+    vector<string> res;
+    for (auto &s : A) {
+      array<int, 26> cnt = {};
+      for (auto c : s)
+        ++cnt[c - 'a'];
+      for (auto i = 0; i < 26; ++i)
+        arr[i] = min(arr[i], cnt[i]);
+    }
+    for (auto i = 0; i < 26; ++i)
+      while (arr[i] != numeric_limits<int>::max() && arr[i]-- > 0)
+        res.push_back(string(1, i + 'a'));
+    return res;
+  }
+};

cpp/100.SameTree/recursion-3ms.cpp

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+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+  // Runtime: 4 ms, faster than 96.40% of C++ online submissions for Construct
+  // Binary Search Tree from Preorder Traversal. Memory Usage: 8.7 MB, less
+  // than 97.42% of C++ online submissions for Construct Binary Search Tree from
+  // Preorder Traversal.
+public:
+  TreeNode *bstFromPreorder(vector<int> &preorder) {
+    if (not preorder.size())
+      return nullptr;
+    auto r = new TreeNode(preorder[0]);
+    auto now = r;
+    vector<TreeNode *> st;
+    for (int i = 1; i < preorder.size(); ++i) {
+      auto t = preorder[i];
+      if (t < now->val) {
+        st.push_back(now);
+        now = now->left = new TreeNode(t);
+      } else {
+        while (st.size() && t > st.back()->val) {
+          now = st.back();
+          st.pop_back();
+        }
+        now = now->right = new TreeNode(t);
+      }
+    }
+    return r;
+  }
+};