feat(codeforces/2108F): add p1/Main.java

Author: lzwjava

codeforces/2108F/src/Main.java

@@ -8,20 +8,20 @@ public class Main {
     BufferedReader in;
     PrintWriter out;
 
-    int[] a;
+    long[] a;
     int n;
-    int maxMEX;
+    long maxMEX;
 
     Main() {
         in = new BufferedReader(new InputStreamReader(System.in));
         out = new PrintWriter(System.out);
     }
 
     void solve() throws IOException {
-        int t = Integer.parseInt(in.readLine());
+        long t = Integer.parseInt(in.readLine());
         while (t-- > 0) {
             n = Integer.parseInt(in.readLine());
-            a = new int[n];
+            a = new long[n];
             StringTokenizer st = new StringTokenizer(in.readLine());
             for (int i = 0; i < n; i++) {
                 a[i] = Integer.parseInt(st.nextToken());
@@ -43,10 +43,10 @@ void printArray(int[] p) {
 
     void permutation(int[] p, boolean[] used, int cur) {
         if (cur == n) {
-            int[] b = a.clone();
+            long[] b = a.clone();
             for (int i = 0; i < n; i++) {
                 int pos = p[i];
-                int bpi = b[pos];
+                long bpi = b[pos];
                 for (int j = 0; j < bpi; j++) {
                     if (pos + j + 1 < n) {
                         b[pos + j + 1] += 1;
@@ -65,11 +65,11 @@ void permutation(int[] p, boolean[] used, int cur) {
             }
 
             if (nonDecreasing) {
-                Set<Integer> set = new HashSet<>();
+                Set<Long> set = new HashSet<>();
                 for (int i = 0; i < n; i++) {
                     set.add(b[i]);
                 }
-                int mex;
+                long mex;
                 for (mex = 1; ; mex++) {
                     if (!set.contains(mex)) {
                         break;
@@ -102,16 +102,6 @@ void close() throws IOException {
     }
 
     public static void main(String[] args) throws Exception {
-        FileInputStream inStream = null;
-        PrintStream outStream = null;
-        boolean isLocal = System.getProperty("os.name").equals("Mac OS X");
-        if (isLocal) {
-            inStream = new FileInputStream("1.in");
-            // outStream = new PrintStream("1.out");
-            System.setIn(inStream);
-            // System.setOut(outStream);
-        }
-
         Main main = new Main();
         main.solve();
         main.close();

codeforces/2108F/src/p1/Main.java

@@ -0,0 +1,78 @@
+package p1;
+
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    BufferedReader in;
+    PrintWriter out;
+
+    Main() {
+        in = new BufferedReader(new InputStreamReader(System.in));
+        out = new PrintWriter(System.out);
+    }
+
+    void solve() throws IOException {
+        int t = Integer.parseInt(in.readLine().trim());
+        while (t-- > 0) {
+            int n = Integer.parseInt(in.readLine().trim());
+            long[] a = new long[n];
+            StringTokenizer st = new StringTokenizer(in.readLine());
+            for (int i = 0; i < n; i++) {
+                if (!st.hasMoreTokens()) {
+                    throw new IOException("Insufficient input tokens");
+                }
+                a[i] = Long.parseLong(st.nextToken());
+                if (a[i] > n) a[i] = n; // Cap a[i] at n
+            }
+
+            // Handle n = 1 separately
+            if (n == 1) {
+                out.println(1); // Final array is [0], MEX = 1
+                continue;
+            }
+
+            // Difference array for range updates
+            long[] diff = new long[n + 1];
+            for (int i = n - 1; i >= 0; i--) {
+                if (a[i] == 0) continue; // No increments if a[i] = 0
+                int start = i + 1;
+                int end = (int) Math.min((long) i + a[i], n - 1);
+                if (start <= end) {
+                    diff[start]++;
+                    if (end + 1 <= n) diff[end + 1]--;
+                }
+            }
+
+            // Compute final array b
+            long[] b = new long[n];
+            long sum = 0;
+            for (int i = 0; i < n; i++) {
+                sum += diff[i];
+                b[i] = sum;
+            }
+
+            // Compute MEX efficiently
+            long mex = 0;
+            for (int i = 0; i < n; i++) {
+                if (b[i] > mex) break; // Gap found
+                if (b[i] == mex) mex++; // All values up to mex-1 exist
+            }
+            out.println(mex);
+        }
+    }
+
+    void close() throws IOException {
+        if (in != null) in.close();
+        if (out != null) {
+            out.flush();
+            out.close();
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        Main main = new Main();
+        main.solve();
+        main.close();
+    }
+}