[ys-han00] WEEK 12 solutions

non-overlapping-intervals/ys-han00.cpp

@@ -0,0 +1,19 @@
+class Solution {
+public:
+    static bool comp(const vector<int> &a, const vector<int> &b) {
+        return (a[1] == b[1] ? a[0] > b[0] : a[1] < b[1]);
+    }
+    int eraseOverlapIntervals(vector<vector<int>>& intervals) {
+        sort(intervals.begin(), intervals.end(), comp);
+        int ans = 0, prev_end = intervals[0][1], start, end;
+        for(int i = 1; i < intervals.size(); i++) {
+            if(prev_end > intervals[i][0]) 
+                ans++;
+            else
+                prev_end = intervals[i][1];
+        }
+
+        return ans;
+    }
+};
+

remove-nth-node-from-end-of-list/ys-han00.cpp

@@ -0,0 +1,53 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* removeNthFromEnd(ListNode* head, int n) {
+        ListNode* first = head;
+        for(int i = 0; i < n; i++)
+            first = first->next;
+
+        ListNode* dummy = new ListNode(-1, head);
+        ListNode* second = dummy;
+        while(first != nullptr) {
+            first = first->next;
+            second = second->next;
+        }
+
+        second->next = second->next->next;
+        return dummy->next;
+    }
+
+    // ListNode* removeNthFromEnd(ListNode* head, int n) {
+    //     stack<ListNode*> sta;
+    //     ListNode* curr = head;
+
+    //     while(curr) {
+    //         sta.push(curr);
+    //         curr = curr->next;
+    //     }
+
+    //     ListNode* prev = nullptr;
+    //     while(n > 1) {
+    //         n--;
+    //         prev = sta.top();
+    //         sta.pop();
+    //     }
+    //     sta.pop();
+    //     if(sta.empty())
+    //         return prev;
+    //     else {
+    //         sta.top()->next = prev;
+    //         return head;
+    //     }
+    // }
+};
+

same-tree/ys-han00.cpp

@@ -0,0 +1,31 @@
+/**
+ * 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 ans = true;
+    void rec(TreeNode* p, TreeNode* q) {
+        if(p == nullptr && q == nullptr)
+            return;
+        else if(p && q && p->val == q->val) {
+            rec(p->left, q->left);
+            rec(p->right, q->right);
+        }
+        else 
+            ans = false;
+    }
+
+    bool isSameTree(TreeNode* p, TreeNode* q) {
+        rec(p, q);
+        return ans;
+    }
+};
+

serialize-and-deserialize-binary-tree/ys-han00.cpp

@@ -0,0 +1,92 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Codec {
+public:
+
+    // Encodes a tree to a single string.
+    string serialize(TreeNode* root) {
+        queue<TreeNode*> que;
+        string str = "root = [";
+
+        if(root != nullptr) {
+            que.push(root);
+            str += to_string(root->val);
+        }
+
+        while(!que.empty()) {
+            TreeNode* curr = que.front();
+            que.pop();
+            if(curr->left != nullptr) {
+                que.push(curr->left);
+                str += "," + to_string(curr->left->val);
+            }
+            else
+                str += ",null";
+
+            if(curr->right != nullptr) {
+                que.push(curr->right);
+                str += "," + to_string(curr->right->val);
+            }
+            else
+                str += ",null";
+        }
+        str += "]";
+        return str;
+    }
+
+    // Decodes your encoded data to tree.
+    TreeNode* deserialize(string data) {
+        int start = data.find('[') + 1;
+        int end = data.find_last_of(']');
+
+        if (start >= end) return nullptr; 
+
+        string content = data.substr(start, end - start);
+
+        vector<string> nodes;
+        stringstream ss(content);
+        string temp;
+        while (getline(ss, temp, ','))
+            nodes.push_back(temp);
+
+        int idx = 0;
+        TreeNode* root = new TreeNode(stoi(nodes[idx++]));
+        queue<TreeNode*> que;
+        que.push(root);
+
+        while(!que.empty() && idx < nodes.size()) {
+            TreeNode* curr = que.front();
+            que.pop();
+
+            if(nodes[idx] == "null") {
+                curr->left = nullptr;
+                idx++;
+            } else {
+                curr->left = new TreeNode(stoi(nodes[idx++]));
+                que.push(curr->left);
+            }
+
+            if(nodes[idx] == "null") {
+                curr->right = nullptr;
+                idx++;
+            } else {
+                curr->right = new TreeNode(stoi(nodes[idx++]));
+                que.push(curr->right);
+            }
+        }
+
+        return root;
+    }
+};
+
+// Your Codec object will be instantiated and called as such:
+// Codec ser, deser;
+// TreeNode* ans = deser.deserialize(ser.serialize(root));
+