Merge pull request #1796 from geegong/main

[Geegong] WEEK 03 solutions

Author: geegong

decode-ways/Geegong.java

@@ -0,0 +1,81 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class Geegong {
+
+    /**
+     * case 1. decodeMap 에 array 의 각 index 별로 디코딩이 가능한 자릿수를 list 로 관리
+     * 후에 decodeMap 을 dfs 로 순회하면서 조합이 가능한 방법을 찾는 방법
+     * 그러나 Time Limit Exceeded 발생ㅠㅠ
+     * @param s
+     * @return
+     */
+    public int numDecodings(String s) {
+        Map<Integer, List<Integer>> decodeMap = new HashMap<>();
+        char[] charArr = s.toCharArray();
+
+        int prevVal = -1;
+        for (int index=0; index<charArr.length; index++) {
+            String str = String.valueOf(charArr[index]);
+            int currentVal = Integer.valueOf(str);
+
+            if (currentVal == 0 && (prevVal == -1 || prevVal > 2)) {
+                // ex) 02xxxx.. , 30xxxx, 1230xxx, 1302xxx
+                // there is no way
+                return 0;
+            } else if (currentVal == 0 && prevVal < 3 && prevVal > 0) {
+                appendDigitNumbers(decodeMap, index - 1, 2, true);
+            } else if (currentVal > 0) {
+                appendDigitNumbers(decodeMap, index, 1, false);
+
+                if (prevVal == 2 && currentVal < 7) {
+                    // for maximum 26
+                    appendDigitNumbers(decodeMap, index - 1, 2, false);
+                } else if (prevVal > 0 && prevVal < 2) {
+                    appendDigitNumbers(decodeMap, index - 1, 2, false);
+                }
+
+            }
+
+            prevVal = currentVal;
+        }
+
+
+        // judge ways
+        return dfs(decodeMap, 0);
+
+    }
+
+    public int dfs(Map<Integer, List<Integer>> decodeMap, int index) {
+        // 자릿수 끝이면 끝
+        if (index > decodeMap.keySet().size() - 1) {
+            return 1;
+        }
+
+        int totalWays = 0;
+        if (decodeMap.containsKey(index)) {
+            List<Integer> waysDigitNumbers = decodeMap.get(index);
+
+            for (Integer digit : waysDigitNumbers) {
+                totalWays += dfs(decodeMap, index + digit);
+            }
+        }
+
+        return totalWays;
+    }
+
+    public void appendDigitNumbers(Map<Integer, List<Integer>> decodeMap, int index, int digitNumber, boolean forceNewWays) {
+        if (!decodeMap.containsKey(index) || forceNewWays) {
+            List<Integer> waysDigitNumber = new ArrayList<>();
+            waysDigitNumber.add(digitNumber);
+            decodeMap.put(index, waysDigitNumber);
+        } else {
+            List<Integer> waysDigitNumber = decodeMap.get(index);
+            waysDigitNumber.add(digitNumber);
+            decodeMap.put(index, waysDigitNumber);
+        }
+    }
+    
+}