feat: 문제풀이 추가

Author: JEONGHWANMIN

kth-smallest-element-in-a-bst/hwanminini.js

@@ -0,0 +1,29 @@
+// 시간 복잡도: O(n)
+// 공간 복잡도: O(n)
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} k
+ * @return {number}
+ */
+var kthSmallest = function(root, k) {
+    const results = []
+
+    const dfs = (tree) => {
+        results.push(tree.val)
+        if (tree.left) dfs(tree.left)
+        if (tree.right) dfs(tree.right)
+    }
+
+    dfs(root)
+
+    return results[k-1]
+};

palindromic-substrings/hwanminini.js

@@ -0,0 +1,35 @@
+// 시간 복잡도: O(n^3)
+// 공간 복잡도: O(1)
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var countSubstrings = function(s) {
+    let count = 0;
+
+    let plusIndex = 0;
+    while (plusIndex !== s.length) {
+        for (let i = 0 ; i < s.length - plusIndex; i++) {
+            if (isValidSubstring(s, i, i + plusIndex)) count++
+        }
+
+        plusIndex++;
+    }
+
+    return count;
+};
+
+
+function isValidSubstring(s, left, right) {
+    while (left <= right) {
+        if (s[left] !== s[right]) return false;
+
+        left++;
+        right--;
+    }
+    return true;
+}
+
+console.log(countSubstrings("abc"));
+console.log(countSubstrings("aaa"));