[재호] WEEK 01 solutions

contains-duplicate/wogha95.js

@@ -0,0 +1,10 @@
+// TC: O(N)
+// SC: O(N)
+
+/**
+ * @param {number[]} nums
+ * @return {boolean}
+ */
+var containsDuplicate = function (nums) {
+  return nums.length !== new Set(nums).size;
+};

kth-smallest-element-in-a-bst/wogha95.js

@@ -0,0 +1,41 @@
+// TC: O(N)
+// SC: 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) {
+  let result = null;
+
+  dfs(root);
+
+  return result;
+
+  function dfs(current) {
+    if (result !== null) {
+      return;
+    }
+    if (!current) {
+      return;
+    }
+
+    dfs(current.left);
+    if (current.val >= 0) {
+      if (k === 1) {
+        result = current.val;
+      }
+      k -= 1;
+    }
+    dfs(current.right);
+  }
+};

number-of-1-bits/wogha95.js

@@ -0,0 +1,13 @@
+// TC: O(log n)
+// SC: O(1)
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var hammingWeight = function (n) {
+  return n
+    .toString(2)
+    .split("")
+    .filter((s) => s === "1").length;
+};

palindromic-substrings/wogha95.js

@@ -0,0 +1,32 @@
+// TC: O(n^3)
+// SC: O(1)
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var countSubstrings = function(s) {
+  let count = 0;
+
+  for (let left = 0; left < s.length; left++) {
+      for (let right = left; right < s.length; right++) {
+          if(checkIsPalinDrome(left, right)) {
+              count += 1;
+          }
+      }
+  }
+
+  return count;
+
+  function checkIsPalinDrome(left, right) {
+      while (left < right) {
+          if (s[left] !== s[right]) {
+              return false;
+          }
+          left += 1;
+          right -= 1;
+      }
+
+      return true;
+  }
+};

top-k-frequent-elements/wogha95.js

@@ -0,0 +1,19 @@
+// TC: O(n logn)
+// SC: O(N)
+
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var topKFrequent = function (nums, k) {
+  const numAndCountBoard = nums.reduce((result, current) => {
+    result[current] = result.hasOwnProperty(current) ? result[current] + 1 : 1;
+    return result;
+  }, {});
+
+  return Object.entries(numAndCountBoard)
+    .sort((a, b) => b[1] - a[1])
+    .slice(0, k)
+    .map((element) => element[0]);
+};