33-kokeunho

kokeunho/README.md

@@ -32,4 +32,5 @@
 | 29차시 | 2025.07.21 | 그래프 탐색 | [불!](https://www.acmicpc.net/problem/4179) |[#118](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/118) |
 | 30차시 | 2025.07.26 | 그래프 탐색 | [중량제한](https://www.acmicpc.net/problem/1939) |[#120](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/120) |
 | 31차시 | 2025.08.03 | 그래프 탐색 | [면접보는 승범이네](https://www.acmicpc.net/problem/17835) | [#126](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/126) |
+| 33차시 | 2025.08.18 | 구현 | [수식 복원하기](https://school.programmers.co.kr/learn/courses/30/lessons/340210) | [#132](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/132) |
 ---

kokeunho/구현/33-kokeunho.java

@@ -0,0 +1,108 @@
+import java.util.*;
+
+class Solution {
+    public String[] solution(String[] expressions) {
+        //최소 가능 진법 찾고 X 포함된 식 따로 분리하기
+        List<String> exprIncludeX = new ArrayList<>();
+        int minBase = 2;
+        for (String expr : expressions) {
+            String[] parts = expr.split(" ");
+            minBase = Math.max(minBase, calculateMinBase(parts[0], parts[2], parts[4]));
+            if (parts[4].equals("X")) exprIncludeX.add(expr);
+        }
+        //가능한 진법들 중 식에 대입하여 검증되는 진법만 추리기
+        List<Integer> candBases = new ArrayList<>();
+        for (int base = minBase; base <= 9; base++) {
+            boolean allValid = true;
+            for (String expr : expressions) {
+                String[] parts = expr.split(" ");
+                if (parts[4].equals("X")) continue;
+                if (!isValidExpression(parts[0], parts[2], parts[4], parts[1], base)) {
+                    allValid = false;
+                    break;
+                }
+            }
+            if (allValid) {
+                candBases.add(base);
+            }
+        }
+        // X 값 구하기
+        String[] results = new String[exprIncludeX.size()];
+        for (int i = 0; i < exprIncludeX.size(); i++) {
+
+            String[] parts = exprIncludeX.get(i).split(" ");
+
+            Set<String> possibleResults = new HashSet<>();
+            for (int base : candBases) {
+                int numA = toBase(parts[0], base);
+                int numB = toBase(parts[2], base);
+                int resultPerBase = switch(parts[1]) {
+                    case "+" -> numA + numB;
+                    case "-" -> numA - numB;
+                    default -> throw new IllegalArgumentException(parts[1]);
+                };
+
+                possibleResults.add(fromBase(resultPerBase, base));
+            }
+            if (possibleResults.size() == 1) {
+                results[i] = parts[0] + " " + parts[1] + " " + parts[2] + " = " + possibleResults.iterator().next();
+            } else {
+                results[i] = parts[0] + " " + parts[1] + " " + parts[2] + " = ?";
+            }
+        }
+        return results;
+    }
+    //가능한 진법 중 최소 진법을 찾기
+    public int calculateMinBase(String... nums) {
+        int response = 2;
+        for (String num : nums) {
+            for (char c : num.toCharArray()) {
+                if (c != 'X') {
+                    int digit = c - '0';
+                    response = Math.max(response, digit+1);
+                }
+            }
+        }
+        return response;
+    }
+    //수식에 해당 진법이 성립하는지 확인
+    public boolean isValidExpression(String a, String b, String c, String op, int base) {
+        int numA = toBase(a, base);
+        int numB = toBase(b, base);
+        int numC = toBase(c, base);
+
+        return switch(op) {
+            case "+" -> numA + numB == numC;
+            case "-" -> numA - numB == numC;
+            default -> false;
+        };
+    }
+    //base 진법의 수를 10진법으로 수정
+    public int toBase(String num, int base) {
+        int result = 0;
+        int power = 1;
+        for (int i = num.length() - 1; i >= 0; i--) {
+            int digit = num.charAt(i) - '0';
+            result += digit * power;
+            power *= base;
+        }
+        return result;
+    }
+    //10진법의 수를 base진법으로 수정
+    public String fromBase(int num, int base) {
+        if (num == 0) return "0";
+
+        //num이 음수인 경우
+        boolean negative = num < 0;
+        if (negative) num = -num;
+
+        StringBuilder result = new StringBuilder();
+        while (num > 0) {
+            result.append(num % base);
+            num /= base;
+        }
+        if (negative) result.append("-");
+
+        return result.reverse().toString();
+    }
+}