[hyunolike] WEEK 05 Solutions

best-time-to-buy-and-sell-stock/hyunolike.java

@@ -0,0 +1,14 @@
+class Solution {
+    public int maxProfit(int[] prices) {
+        // 주식 최대 이익
+        int minPrice = Integer.MAX_VALUE;
+        int maxProfit = 0;
+
+        for (int price : prices) {
+            minPrice = Math.min(minPrice, price);
+            maxProfit = Math.max(maxProfit, price - minPrice);
+        }
+
+        return maxProfit;
+    }
+}

encode-and-decode-strings/hyunolike.java

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+public class Codec {
+
+    // Encodes a list of strings to a single string.
+    public String encode(List<String> strs) {
+        StringBuilder sb = new StringBuilder();
+
+        for (String s : strs) {
+            sb.append(s.length()).append('#').append(s);
+        }
+
+        return sb.toString();
+    }
+
+    // Decodes a single string to a list of strings.
+    public List<String> decode(String s) {
+        List<String> res = new ArrayList<>();
+        int i = 0;
+
+        while (i < s.length()) {
+            int j = i;
+
+            // find '#'
+            while (s.charAt(j) != '#') {
+                j++;
+            }
+
+            int length = Integer.parseInt(s.substring(i, j));
+            j++; // move past '#'
+
+            String word = s.substring(j, j + length);
+            res.add(word);
+
+            i = j + length; // move to next encoded segment
+        }
+
+        return res;
+    }
+}
+

group-anagrams/hyunolike.java

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+class Solution {
+    public List<List<String>> groupAnagrams(String[] strs) {
+        // 같은 문자열 끼리 묶기
+        // 그룹이 가장 적은 순으로 정렬
+
+        Map<String, List<String>> map = new HashMap<>();
+
+        // 각 문자열 char로 바꿔서 정렬하고 다시 문자열
+        for(String str : strs) {
+            char[] arr = str.toCharArray();
+            Arrays.sort(arr);
+
+            String key = new String(arr); // 정렬된 문자열 키로 하기
+
+            map.computeIfAbsent(key, k -> new ArrayList<>()).add(str);
+        }
+
+        return new ArrayList<>(map.values());
+        // map 자료구조, 정렬까지 생각 
+        // 이후 프로세스 생각 어려움
+    }
+}

implement-trie-prefix-tree/hyunolike.java

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+class TrieNode {
+    TrieNode[] children = new TrieNode[26];
+    boolean isEnd;
+}
+
+class Trie {
+
+    private TrieNode root;
+
+    public Trie() {
+        root = new TrieNode();
+    }
+
+    public void insert(String word) {
+        TrieNode node = root;
+        for (char c : word.toCharArray()) {
+            int idx = c - 'a';
+            if(node.children[idx] == null) {
+                node.children[idx] = new TrieNode();
+            }
+            node = node.children[idx];
+        }
+        node.isEnd = true;
+    }
+
+    public boolean search(String word) {
+        TrieNode node = root;
+        for(char c : word.toCharArray()) {
+            int idx = c - 'a'; 
+            if(node.children[idx] == null) return false;
+            node = node.children[idx];
+        }
+
+        return node.isEnd;
+    }
+
+    public boolean startsWith(String prefix) {
+        TrieNode node = root;
+        for(char c : prefix.toCharArray()) {
+            int idx = c - 'a';
+            if(node.children[idx] == null) return false;
+            node = node.children[idx];
+        }
+        return true;
+    }
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * Trie obj = new Trie();
+ * obj.insert(word);
+ * boolean param_2 = obj.search(word);
+ * boolean param_3 = obj.startsWith(prefix);
+ */
+

word-break/hyunolike.java

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+class Solution {
+    public boolean wordBreak(String s, List<String> wordDict) {
+        int n = s.length();
+        boolean[] dp = new boolean[n+1];
+        dp[0] = true;
+
+        Set<String> wordSet = new HashSet<>(wordDict);
+
+        for(int i = 1; i <= n; i++) {
+            for(int j = 0; j < i; j++) {
+                if(dp[j] && wordSet.contains(s.substring(j, i))) {
+                    dp[i] = true;
+                    break;
+                }
+            }
+        }
+        return dp[n];
+    }
+}
+

word-break/hyunolike.ts

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+function wordBreak(s: string, wordDict: string[]): boolean {
+    const n = s.length;
+    const dp:boolean[] = Array(n+1).fill(false);
+    dp[0] = true;
+
+    const wordSet = new Set(wordDict);
+
+    for(let i = 1; i <= n; i++) {
+        for(let j = 0; j < i; j++) {
+            if(dp[j] && wordSet.has(s.substring(j, i))) {
+                dp[i] = true;
+                break;
+            }
+        }
+    }
+    return dp[n];
+};