[YoungSeok-Choi] Week 5 Solutions

best-time-to-buy-and-sell-stock/YoungSeok-Choi.java

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+// NOTE: tc --> O(n)
+class Solution {
+    public int maxProfit(int[] prices) {
+
+        int curMax = 0;
+        int gMax = 0;
+
+        if(prices.length == 0) return 0;
+
+        int sell = prices[0];
+        for(int i = 1; i < prices.length; i++) {
+            curMax = Math.max(0, prices[i] - sell);
+
+            // NOTE: 새롭게 시작하는게 더 좋은경우
+            if(curMax == 0) {
+                sell = prices[i];
+            }
+
+            gMax = Math.max(curMax, gMax); 
+        }
+
+        return gMax;        
+    }
+}

encode-and-decode-strings/YoungSeok-Choi.java

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+import java.util.ArrayList;
+import java.util.List;
+
+public class Solution {
+    /*
+     * @param strs: a list of strings
+     * @return: encodes a list of strings to a single string.
+     */
+    public String encode(List<String> strs) {
+        List<String> temp = new ArrayList<>();
+
+        if(strs.size() == 0) return null;
+
+        for(String s : strs) {
+            if(":".equals(s)) {
+                temp.add("::");
+            } else {
+                temp.add(s);
+            }            
+        }
+
+        return String.join(":;", temp);
+    }
+
+    /*
+     * @param str: A string
+     * @return: decodes a single string to a list of strings
+     */
+    public List<String> decode(String str) {
+        List<String> temp = new ArrayList<>();
+
+        if(str == null) return new ArrayList<>();
+
+        // if(str.length() == 0) return new ArrayList<>();
+
+        for(String s : str.split(":;")) {
+            if("::".equals(s)) {
+                temp.add(":");
+            } else {
+                temp.add(s);
+            }            
+        }
+        return temp;
+    }
+}

group-anagrams/YoungSeok-Choi.java

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+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+// NOTE: tc -> O(n)
+class Solution {
+    public List<List<String>> groupAnagrams(String[] strs) {
+
+        List<List<String>> result = new ArrayList<>();
+        Map<String, List<String>> sMap = new HashMap<>();
+
+        for(int i = 0; i < strs.length; i++) {
+            char[] cArr = strs[i].toCharArray();
+            Arrays.sort(cArr);
+            String sorted = new String(cArr);
+
+            if(sMap.containsKey(sorted)) {
+                sMap.get(sorted).add(strs[i]);
+            } else {
+                List<String> temp = new ArrayList<>();
+                temp.add(strs[i]);
+                sMap.put(sorted, temp);
+            }
+        }
+
+        for(List<String> arr : sMap.values()) {
+            result.add(arr);
+        }
+
+        return result;
+    }
+}