add prob #637; iterative solution

Author: randomwalk10

637_Average_of_Levels_in_Binary_Tree_2nd.cpp

@@ -0,0 +1,52 @@
+#include <vector>
+#include <stack>
+using namespace std;
+
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+
+class Solution {
+public:
+    vector<double> averageOfLevels(TreeNode* root) {
+		if(root==NULL) return {};
+		stack<TreeNode*> s_parent;
+		stack<int> s_depth;
+		vector<double> sums;
+		vector<int> counts;
+
+		s_parent.push(root);
+		s_depth.push(1);
+		while(!s_parent.empty()){
+			TreeNode* tmp_node = s_parent.top(); s_parent.pop();
+			int tmp_depth = s_depth.top(); s_depth.pop();
+
+			if(tmp_depth>(int)sums.size()){
+				sums.push_back((double)(tmp_node->val));
+				counts.push_back(1);
+			}
+			else{
+				sums[tmp_depth-1] += (double)(tmp_node->val);
+				counts[tmp_depth-1] += 1;
+			}
+
+			if(tmp_node->right){
+				s_parent.push(tmp_node->right);
+				s_depth.push(tmp_depth+1);
+			}
+			if(tmp_node->left){
+				s_parent.push(tmp_node->left);
+				s_depth.push(tmp_depth+1);
+			}
+		}
+
+		for (int i = 0; i < (int)sums.size(); ++i) {
+			sums[i] /= counts[i];
+		}
+
+		return sums;
+    }
+};