[20250616] BOJ / G2 / 합이 0인 네 정수 / 이강현

lkhyun/202506/16 BOJ G2 합이 0인 네 정수.md

@@ -0,0 +1,69 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static int N;
+    static int[] A;
+    static int[] B;
+    static int[] C;
+    static int[] D;
+    static int[] AB;
+    static int[] CD;
+    static long answer = 0;
+
+    public static void main(String[] args) throws IOException {
+        N = Integer.parseInt(br.readLine());
+        A = new int[N];
+        B = new int[N];
+        C = new int[N];
+        D = new int[N];
+        for (int i = 0; i < N; i++) {
+            st = new StringTokenizer(br.readLine());
+            A[i] = Integer.parseInt(st.nextToken());
+            B[i] = Integer.parseInt(st.nextToken());
+            C[i] = Integer.parseInt(st.nextToken());
+            D[i] = Integer.parseInt(st.nextToken());
+        }
+
+        AB = new int[N*N];
+        CD = new int[N*N];
+        for (int i = 0; i < N; i++) {
+            for (int j = 0; j < N; j++) {
+                AB[i*N+j] = A[i] + B[j];
+                CD[i*N+j] = C[i] + D[j];
+            }
+        }
+        Arrays.sort(AB);
+        Arrays.sort(CD);
+
+        int left = 0, right = N*N-1;
+        while (left < N*N && right >= 0) {
+            if(AB[left] + CD[right] == 0){
+                int leftCnt = 1;
+                while(left + 1 < N*N && AB[left+1] == AB[left]){
+                    left++;
+                    leftCnt++;
+                }
+                int rightCnt = 1;
+                while(right - 1 >= 0 && CD[right-1] == CD[right]){
+                    right--;
+                    rightCnt++;
+                }
+                answer += (long)leftCnt * rightCnt;
+                left++;
+                right--;
+            }else if(AB[left] + CD[right] < 0){
+                left++;
+            }else{
+                right--;
+            }
+        }
+        bw.write(answer + "\n");
+        bw.close();
+    }
+}
+```