Create yeongu.cpp

Author: YeonguChoe

kth-smallest-element-in-a-bst/yeongu.cpp

@@ -0,0 +1,27 @@
+TC: O(n log n) 왜냐하면, heap에 push연산이 log n이고 각 노드마다 실행하므로.
+SC: O(n) queue가 n까지 커질수 있음.
+
+    int kthSmallest(TreeNode* root, int k) {
+        priority_queue<int, vector<int>, greater<int>> minHeap;
+
+        // bfs
+        queue<TreeNode*> q;
+        if (root != nullptr) {
+            q.push(root);
+        };
+        while (!q.empty()) {
+            minHeap.push(q.front()->val);
+            if (q.front()->left != nullptr) {
+                q.push(q.front()->left);
+            }
+            if (q.front()->right != nullptr) {
+                q.push(q.front()->right);
+            }
+            q.pop();
+        }
+
+        for (int i = 0; i < k - 1; i++) {
+            minHeap.pop();
+        }
+        return minHeap.top();
+    }