[lhc0506] WEEK 05 solutions

best-time-to-buy-and-sell-stock/lhc0506.js

@@ -0,0 +1,15 @@
+/**
+ * @param {number[]} prices
+ * @return {number}
+ */
+var maxProfit = function(prices) {
+    let minPrice = Number.MAX_SAFE_INTEGER;
+    let maxProfit = 0;
+
+    for (let i = 0; i < prices.length; i++) {
+        minPrice = Math.min(minPrice, prices[i]);
+        maxProfit = Math.max(maxProfit, prices[i] - minPrice);
+    }
+
+    return maxProfit;
+};

encode-and-decode-strings/lhc0506.js

@@ -0,0 +1,17 @@
+class Solution {
+    /**
+     * @param {string[]} strs
+     * @returns {string}
+     */
+    encode(strs) {
+        return JSON.stringify(strs);
+    }
+
+    /**
+     * @param {string} str
+     * @returns {string[]}
+     */
+    decode(str) {
+        return JSON.parse(str);
+    }
+}

group-anagrams/lhc0506.js

@@ -0,0 +1,33 @@
+/**
+ * @param {string[]} strs
+ * @return {string[][]}
+ */
+var groupAnagrams = function(strs) {
+    const A_ASCII = 'a'.charCodeAt();
+
+    const anagramMap = new Map();
+
+    for (const str of strs) {
+        const counter = new Array(26).fill(0);
+
+        for (let i = 0; i < str.length; i++) {
+            counter[str.charCodeAt(i) - A_ASCII]++;
+        }
+
+        let key = '';
+        for (let i = 0; i < 26; i++) {
+            if (counter[i] > 0) {
+                key += String.fromCharCode(i + A_ASCII) + counter[i];
+            }
+        }
+
+        if (!anagramMap.has(key)) {
+            anagramMap.set(key, []);
+        }
+        anagramMap.get(key).push(str);
+    }
+
+    return Array.from(anagramMap.values());
+};
+
+// 시간 복잡도: O(n), 공간 복잡도: O(n)

implement-trie-prefix-tree/lhc0506.js

@@ -0,0 +1,65 @@
+
+var Trie = function() {
+    this.isEnd = false;
+};
+
+/**
+ * @param {string} word
+ * @return {void}
+ */
+Trie.prototype.insert = function(word) {
+    let currentTrie = this;
+    word.split('').forEach(alphabet => {
+        if (!currentTrie[alphabet]) {
+            currentTrie[alphabet] = new Trie();
+        }
+        currentTrie = currentTrie[alphabet];
+    });
+
+    currentTrie.isEnd = true;
+};
+
+/**
+ * @param {string} word
+ * @return {boolean}
+ */
+Trie.prototype.search = function(word) {
+    let currentTrie = this;
+
+    for (let alphabet of word) {
+        if (!currentTrie[alphabet]) {
+            return false;
+        }
+        currentTrie = currentTrie[alphabet];
+    }
+
+    return currentTrie.isEnd;
+};
+
+/**
+ * @param {string} prefix
+ * @return {boolean}
+ */
+Trie.prototype.startsWith = function(prefix) {
+    let currentTrie = this;
+
+    for (let alphabet of prefix) {
+        if (!currentTrie[alphabet]) {
+            return false;
+        }
+        currentTrie = currentTrie[alphabet];
+    }
+
+    return true;
+};
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * var obj = new Trie()
+ * obj.insert(word)
+ * var param_2 = obj.search(word)
+ * var param_3 = obj.startsWith(prefix)
+ */
+
+
+// insert 시간복잡도: O(n), search 시간복잡도: O(n), startsWith 시간복잡도: O(n)

word-break/lhc0506.js

@@ -0,0 +1,29 @@
+/**
+ * @param {string} s
+ * @param {string[]} wordDict
+ * @return {boolean}
+ */
+var wordBreak = function(s, wordDict) {
+    const wordDictSet = new Set(wordDict);
+    const visited = new Set();
+
+    const indexStack = [0];
+    while(indexStack.length > 0) {
+        const startIndex = indexStack.pop();
+
+        if (visited.has(startIndex)) continue;
+        visited.add(startIndex);
+
+        if (startIndex === s.length) return true;
+
+        for (let endIndex = startIndex + 1; endIndex <= s.length; endIndex++) {
+            const word = s.substring(startIndex, endIndex);
+
+            if (wordDictSet.has(word)) {
+                indexStack.push(endIndex);
+            }
+        }
+    }
+
+    return false;
+};