Day-7

Author: shumbul

Day-07/39. Swap Nodes in Pairs.cpp

@@ -0,0 +1,26 @@
+// Link - https://leetcode.com/problems/swap-nodes-in-pairs/
+// Author - Shumbul Arifa
+
+/**
+ * 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* swapPairs(ListNode* head) {
+		auto tmp = head;
+		while (tmp && tmp->next) {
+			int t = tmp->val;
+			tmp->val = tmp->next->val;
+			tmp->next->val = t;
+			tmp = tmp->next->next;
+		}
+		return head;
+	}
+};

Day-07/40. Flatten Binary Tree to Linked List.cpp

@@ -0,0 +1,29 @@
+// Link - https://leetcode.com/problems/flatten-binary-tree-to-linked-list/
+// Author - Shumbul Arifa
+
+/**
+ * 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 {
+	TreeNode* prev = NULL;
+public:
+	void flatten(TreeNode* root) {
+		if (!root)
+			return;
+		if (root->right)
+			flatten(root->right);
+		if (root->left)
+			flatten(root->left);
+		root->right = prev;
+		root->left = NULL;
+		prev = root;
+	}
+};

Day-07/41. Partition List.cpp

@@ -0,0 +1,41 @@
+// Link - https://leetcode.com/problems/partition-list/
+// Author - Shumbul Arifa
+
+/**
+ * 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* partition(ListNode* head, int x) {
+		if (!head)
+			return head;
+		ListNode* l1 = new ListNode(0), *l2 = new ListNode(0);
+		auto t1 = l1;
+		auto t2 = l2;
+		if (!l1 || !l2)
+			return head;
+		while (head) {
+			// cout<<head->val<<"\n";
+			if (head->val < x) {
+				t1->next = head;
+				t1 = t1->next;
+			}
+			else {
+				t2->next = head;
+				t2 = t2->next;
+			}
+			head = head->next;
+		}
+		t1->next = NULL;
+		t2->next = NULL;
+		t1->next = l2->next;
+		return l1->next;
+	}
+};

README.md

@@ -74,4 +74,12 @@
 35. [Symmetric Tree](https://leetcode.com/problems/symmetric-tree/)
 36. [Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/)
 37. [Subtree of Another Tree](https://leetcode.com/problems/subtree-of-another-tree/)
-38. [Path Sum](https://leetcode.com/problems/path-sum/)
+38. [Path Sum](https://leetcode.com/problems/path-sum/)
+
+## Day-07
+09/09/21
+3 problems
+
+39. [Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)
+40. [Flatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/)
+41. [Partition List](https://leetcode.com/problems/partition-list/)