[나리] WEEK04 Solutions

missing-number/naringst.js

@@ -0,0 +1,62 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+
+/**
+ * Runtime: 63ms, Memory: 51.68MB
+ * Time complexity: O(nlogn)
+ * Space complexity: O(nlogn)
+ *
+ */
+
+var missingNumber = function (nums) {
+  const n = nums.length;
+  nums.sort((a, b) => a - b);
+
+  if (!nums.includes(0)) {
+    return 0;
+  }
+  for (let i = 0; i < n; i++) {
+    if (nums[i + 1] - nums[i] !== 1) {
+      return nums[i] + 1;
+    }
+  }
+  return nums[-1];
+};
+
+/**
+ * NOTE
+ * if use 'sort()' -> O(nlogn)
+ * if you solve this problem without using sort(), can use sum of nums
+ */
+
+var missingNumber = function (nums) {
+  const sumOfNums = nums.reduce((num, total) => num + total, 0);
+
+  const n = nums.length;
+  const expectedSum = (n * (n + 1)) / 2;
+
+  if (expectedSum === sumOfNums) {
+    return 0;
+  } else {
+    return expectedSum - sumOfNums;
+  }
+};
+
+/**
+ * NOTE
+ * or you can subtract while adding
+ */
+
+var missingNumber = function (nums) {
+  let target = 0;
+  for (let i = 0; i <= nums.length; i++) {
+    target += i;
+
+    if (i < nums.length) {
+      target -= nums[i];
+    }
+  }
+  return target;
+};

valid-palindrome/naringst.js

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+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+
+/**
+ * Runtime: 66ms, Memory: 54.75MB
+ * Time complexity: O(s.length)
+ * Space complexity: O(s.length)
+ *
+ */
+
+var isPalindrome = function (s) {
+  let trimmed = s.toLowerCase();
+  let answer = [];
+  let checkAlphabet = /[a-zA-Z]/;
+  let checkNum = /[0-9]/;
+
+  for (let alpha of trimmed) {
+    if (checkAlphabet.test(alpha) || checkNum.test(alpha)) {
+      answer.push(alpha);
+    }
+  }
+
+  if (answer.join("") === answer.reverse().join("")) {
+    return true;
+  }
+  return false;
+};