Merge pull request #459 from AlgorithmWithGod/03do-new30

[20250714] BOJ / G4 / 좋다 / 신동윤

Author: ShinHeeEul

03do-new30/202507/14 BOJ G4 좋다.md

@@ -0,0 +1,50 @@
+```java
+import java.util.*;
+import java.io.*;
+
+public class Main {
+    static int N, answer;
+    static long[] arr;
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        N = Integer.parseInt(br.readLine());
+        arr = new long[N];
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        for (int i = 0; i < N; i++) {
+            arr[i] = Long.parseLong(st.nextToken());
+        }
+        Arrays.sort(arr);
+        answer = 0;
+        for (int i = 0; i < N; i++) {
+            twoPointer(i);
+        }
+        System.out.println(answer);
+
+        br.close();
+    }
+    private static void twoPointer(int targetIdx) {
+        long target = arr[targetIdx];
+        int leftIdx = 0;
+        int rightIdx = N-1;
+        while (leftIdx < rightIdx) {
+            long sum = arr[leftIdx] + arr[rightIdx];
+            if (target == sum) {
+                if (leftIdx == targetIdx) {
+                    leftIdx++;
+                } else if (rightIdx == targetIdx) {
+                    rightIdx--;
+                } else {
+                    answer++;
+                    return;
+                }
+            }
+            else if (sum < target) {
+                leftIdx++;
+            } else {
+                rightIdx--;
+            }
+        }
+    }
+
+}
+```