add 101, 118, 119

Author: rustykitty

0101-symmetric-tree.cpp

@@ -0,0 +1,32 @@
+/*
+101. Symmetric Tree
+
+Submitted: December 9, 2024
+
+Runtime: 0 ms (beats 100.00%)
+Memory: 18.41 MB (beats 12.19%)
+*/
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    bool isSymmetric(TreeNode* root) {
+        if (root == nullptr) return true;
+        return helper(root->left, root->right);
+    }
+    bool helper(TreeNode* a, TreeNode* b) {
+        if (a == nullptr || b == nullptr) return a == b;
+        if (a->val != b->val) return false;
+        return helper(a->left, b->right) && helper(a->right, b->left);
+    }
+};

0118-pascals-triangle.cpp

@@ -0,0 +1,27 @@
+/*
+118. Pascal's Triangle
+
+Submitted: December 10, 2024
+
+Runtime: 0 ms (beats 100.00%)
+Memory: 9.82 MB (beats 7.86%)
+*/
+
+class Solution {
+public:
+    vector<vector<int>> generate(int numRows) {
+        vector<vector<int>> res;
+        res.push_back({1});
+        for (int i = 1; i < numRows; ++i) {
+            vector<int> t;
+            t.push_back(1);
+            vector<int>& prev = res.back();
+            for (int j = 0, n = prev.size(); j < n - 1; ++j) {
+                t.push_back(prev[j] + prev[j + 1]);
+            }
+            t.push_back(1);
+            res.push_back(t);
+        }
+        return res;
+    }
+};

0119-pascals-triangle-ii.cpp

@@ -0,0 +1,23 @@
+/*
+119. Pascal's Triangle II
+
+Submitted: December 10, 2024
+
+Runtime: 0 ms (beats 100.00%)
+Memory: 9.63 MB (beats 7.45%)
+*/
+
+class Solution {
+public:
+    vector<int> getRow(int rowIndex) {
+        if (rowIndex == 0) return {1};
+        vector<int> prev = getRow(rowIndex - 1);
+        vector<int> res;
+        res.push_back(1);
+        for (int i = 0; i < prev.size() - 1; ++i) {
+            res.push_back(prev[i] + prev[i + 1]);
+        }
+        res.push_back(1);
+        return res;
+    }
+};