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[ganu] Week 5 #845

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Jan 11, 2025
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18 changes: 18 additions & 0 deletions best-time-to-buy-and-sell-stock/gwbaik9717.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
// Time complexity: O(n)
// Space complexity: O(1)

/**
* @param {number[]} prices
* @return {number}
*/
var maxProfit = function (prices) {
let answer = 0;
let minValue = Number.MAX_SAFE_INTEGER;

for (const price of prices) {
minValue = Math.min(minValue, price);
answer = Math.max(answer, price - minValue);
}

return answer;
};
37 changes: 37 additions & 0 deletions encode-and-decode-strings/gwbaik9717.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
// n: len(str)
// Time complexity: O(n)
// Space complexity: O(1)
const encode = function (arr) {
let answer = "";

for (const word of arr) {
answer += `${word.length}${SEPERATOR}`;
}

return answer;
};

// n: len(str)
// Time complexity: O(n)
// Space complexity: O(n)
const decode = function (str) {
const SEPERATOR = "|";
const words = [];

let i = 0;
let wordLength = "";

while (i < str.length) {
if (str[i] === SEPERATOR) {
words.push(str.slice(i + 1, i + 1 + Number(wordLength)));
i += Number(wordLength) + 1;
wordLength = "";
continue;
}

wordLength += str[i];
i += 1;
}

return words;
};
46 changes: 46 additions & 0 deletions group-anagrams/gwbaik9717.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,46 @@
// n: length of strs, m: length of strs[i]
// Time complexity: O(nm)
// Space complexity: O(n)

/**
* @param {string[]} strs
* @return {string[][]}
*/
var groupAnagrams = function (strs) {
const answer = [];
const anagramDict = new Map();

const getKey = (str) => {
const minCharCode = "a".charCodeAt();
const maxCharCode = "z".charCodeAt();

const counter = Array.from(
{ length: maxCharCode - minCharCode + 1 },
() => 0
);

for (const chr of str) {
const index = chr.charCodeAt() - minCharCode;
counter[index]++;
}

return counter.join("#");
};

for (let i = 0; i < strs.length; i++) {
const str = strs[i];
const key = getKey(str);

if (!anagramDict.has(key)) {
anagramDict.set(key, []);
}

anagramDict.get(key).push(str);
}

for (const [_, value] of anagramDict) {
answer.push(value);
}

return answer;
};
79 changes: 79 additions & 0 deletions implement-trie-prefix-tree/gwbaik9717.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,79 @@
var Node = function () {
this.children = new Map();
this.isEnd = false;
};

var Trie = function () {
this.head = new Node();
};

/**
* @param {string} str
* @return {TrieNode | null}
*/
Trie.prototype._traverse = function (str) {
let current = this.head;

for (const chr of str) {
if (!current.children.has(chr)) {
return null;
}
current = current.children.get(chr);
}

return current;
};

/**
* @param {string} word
* @return {void}
*/
Trie.prototype.insert = function (word) {
let current = this.head;

for (const chr of word) {
if (!current.children.has(chr)) {
current.children.set(chr, new Node());
}

current = current.children.get(chr);
}

current.isEnd = true;
};

/**
* @param {string} word
* @return {boolean}
*/
Trie.prototype.search = function (word) {
const node = this._traverse(word);

if (!node) {
return false;
}

return node.isEnd;
};

/**
* @param {string} prefix
* @return {boolean}
*/
Trie.prototype.startsWith = function (prefix) {
const node = this._traverse(prefix);

if (!node) {
return false;
}

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)
*/
25 changes: 25 additions & 0 deletions word-break/gwbaik9717.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
// n: len(s), m: len(wordDict)
// Time complexity: O(n^2*m)
// Space complexity: O(n)

/**
* @param {string} s
* @param {string[]} wordDict
* @return {boolean}
*/
var wordBreak = function (s, wordDict) {
const dp = Array.from({ length: s.length + 1 }, () => false);
dp[0] = true;

for (let i = 1; i <= s.length; i++) {
for (const word of wordDict) {
const sliced = s.slice(i - word.length, i);

if (word === sliced && !dp[i]) {
dp[i] = dp[i - word.length];
}
}
}

return dp.at(-1);
};
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