couple of tree prolems

Author: piyushkhemka

Populating Right Next Pointers in each Node.cpp

@@ -0,0 +1,97 @@
+/**
+ * Definition for binary tree with next pointer.
+ * struct TreeLinkNode {
+ *  int val;
+ *  TreeLinkNode *left, *right, *next;
+ *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
+ * };
+ */
+
+// With extra space. O(n) space. Iterative solution
+class Solution {
+public:
+    void connect(TreeLinkNode *root) {
+
+        if(root == NULL)
+            return;
+
+        queue<TreeLinkNode *> q;
+
+        q.push(root);
+
+        while(!q.empty()) {
+            int num = q.size();
+            while(num) {
+                TreeLinkNode *cur = q.front();
+                q.pop();
+                num--;
+
+                if(num > 0)
+                    cur->next = q.front();
+                else
+                    cur->next = NULL;
+
+                // assign next value
+
+                if(cur->left != NULL)
+                    q.push(cur->left);
+
+                if(cur->right != NULL)
+                    q.push(cur->right);
+            }
+        }
+
+
+    }
+};
+
+
+------
+
+// Recursive solution. Still uses extra space (extra space used to accomodate recursion stack)
+class Solution {
+public:
+    void connect(TreeLinkNode *root) {
+
+        if(!root)
+            return;
+
+        if(root->left) {
+            root->left->next = root->right;
+            if(root->next) {
+                root->right->next = root->next->left;
+            }
+
+        }
+        connect(root->left);
+        connect(root->right);
+    }
+};
+
+-----
+
+// Two pointer method without any extra space
+class Solution {
+public:
+    void connect(TreeLinkNode *root) {
+
+        TreeLinkNode *pre = root;
+        TreeLinkNode *cur = NULL;
+
+        if(root == NULL)
+            return;
+
+        while(pre && pre->left) {
+            cur = pre;
+            while (cur) {
+                cur->left->next = cur->right;
+                if(cur->next) {
+                    cur->right->next = cur->next->left;
+                }
+                cur = cur->next;
+            }
+            pre = pre->left;
+        }
+    }
+
+};

right view of a binary tree.cpp

@@ -0,0 +1,47 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+/*
+Note to self : leveloftree needs to be passed as a pointer. Because otherwise,
+leveloftree takes the value of the previous self in the recursion tree. The line
+leveloftree won't take the value of curlevel unless its state is maintained through a pointer
+The other alternative is to drop the variable leveloftree and use
+result.size() < curlevel
+*/
+
+class Solution {
+
+
+    void printrightsideview(TreeNode *root, int curlevel, int *leveloftree, vector<int> &result) {
+        if(root == NULL)
+            return;
+
+        if(curlevel > *leveloftree ) {
+            result.push_back(root->val);
+            *leveloftree  = curlevel;
+        }
+
+        printrightsideview(root->right,curlevel+1,leveloftree,result);
+        printrightsideview(root->left,curlevel+1,leveloftree,result);
+
+    }
+public:
+
+    vector<int> rightSideView(TreeNode* root) {
+
+        vector<int> result;
+        int m = 0;
+        printrightsideview(root, 1, &m, result);
+        return result;
+
+    }
+
+
+};