[choidabom] WEEK 03 solutions

climbing-stairs/choidabom.js

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+// https://leetcode.com/problems/climbing-stairs/
+
+// TC: O(N)
+// SC: O(N)
+
+var climbStairs = function (n) {
+  const stairs = [1, 2];
+
+  for (let i = 2; i < n; i++) {
+    stairs[i] = stairs[i - 1] + stairs[i - 2];
+  }
+
+  return stairs[n - 1];
+};
+
+console.log(climbStairs(5));

maximum-subarray/choidabom.ts

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+// https://leetcode.com/problems/maximum-subarray/
+
+// Time Limit Exceeded
+function maxSubArray(nums: number[]): number {
+    const acc = []
+    const len = nums.length
+
+    for (let size = 1; size <= len; size++) {
+        for (let start = 0; start <= len - size; start++) {
+            const sub = nums.slice(start, start + size)
+            const sum = sub.reduce((acc, num)=> acc += num, 0)
+            acc.push(sum)
+        }
+    }
+
+    return acc.sort((a, b) => b - a)[0]
+};
+
+// TC: O(n) 
+// SC: O(n)  
+
+function maxSubArray(nums: number[]): number {
+    const dp = [...nums]; 
+    let max = dp[0];
+
+    for (let i = 1; i < nums.length; i++) {
+        dp[i] = Math.max(nums[i], dp[i - 1] + nums[i]);
+        max = Math.max(max, dp[i]);
+    }
+
+    return max;
+}

number-of-1-bits/choidabom.ts

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+// https://leetcode.com/problems/number-of-1-bits/
+
+// TC: O(logN) - n을 2로 나누며 1을 셈 
+// SC: O(1) - 배열을 사용하지 않고, 변수만 사용하여 추가 메모리 x
+
+function hammingWeight(n: number): number {
+    let answer = 0
+
+    while (n > 0) {
+        answer += n % 2
+        n = Math.floor(n / 2)
+    }
+
+    return answer
+}

valid-anagram/choidabom.js

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+// https://leetcode.com/problems/valid-anagram/submissions/1603502655/
+
+// TC: O(NlogN)
+// SC: O(N)
+
+var isAnagram = function (s, t) {
+    return s.split("").sort().join("") === t.split("").sort().join("")
+};
+
+// TC: O(N)
+// SC: O(N)
+
+var isAnagram = function (s, t) {
+    const map = new Map()
+
+    for (const char of s) {
+        if (map.has(char)) map.set(char, map.get(char) + 1)
+        else map.set(char, 1)
+    }
+
+    for (const char of t) {
+        if (!map.has(char)) return false
+        else map.set(char, map.get(char) - 1)
+    }
+
+    for (const value of map.values()) {
+        if (value !== 0) return false
+    }
+
+    return true
+};
+
+console.log(isAnagram(s = "anagram", t = "nagaram"))

valid-palindrome/choidabom.ts

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+// https://leetcode.com/problems/valid-palindrome/
+
+// TC: O(n)
+// SC: O(n)
+
+function isPalindrome(s: string): boolean {
+  const str = (s.toLowerCase().match(/[a-z0-9]/g) || []).join("");
+  const reverse = str.split("").reverse().join("");
+
+  return str === reverse;
+}