Create 111. Minimum Depth of Binary Tree.cpp

Author: NeoYY

Diff for: 111. Minimum Depth of Binary Tree.cpp

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+/*
+Given a binary tree, find its minimum depth.
+
+The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
+
+Note: A leaf is a node with no children.
+
+Example:
+
+Given binary tree [3,9,20,null,null,15,7],
+
+    3
+   / \
+  9  20
+    /  \
+   15   7
+return its minimum depth = 2.
+
+Solution one is recursive, two is iterative.
+*/
+
+/**
+ * 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:
+    int minDepth(TreeNode* root) {
+        if ( !root ) return 0;
+        if ( !root->left ) return minDepth( root->right ) + 1;
+        if ( !root->right ) return minDepth( root->left ) + 1;
+        return min( minDepth( root->left ), minDepth( root->right ) ) + 1;
+    }
+};
+
+class Solution {
+public:
+    int minDepth(TreeNode* root) {
+        if ( !root ) return 0;
+        int depth = 0;
+        int width = 0;
+        queue<TreeNode*> q;
+        TreeNode *temp = root;
+        q.push( temp );
+        while ( !q.empty() )
+        {
+            depth++;
+            width = q.size();
+            for ( int i = 0; i < width; i++ )
+            {
+                temp = q.front();
+                q.pop();                
+                if ( !temp->left && !temp->right ) return depth;
+                if ( temp->left ) q.push( temp->left );
+                if ( temp->right ) q.push( temp->right );   
+            }
+        }
+        return depth;
+    }
+};