feat: add java solution to lc problem: No.3009 (doocs#2395)

No.3009.Maximum Number of Intersections on the Chart

Author: priyanshun2017

solution/3000-3099/3009.Maximum Number of Intersections on the Chart/README.md

@@ -53,7 +53,28 @@
 ```
 
 ```java
-
+class Solution {
+    public int maxIntersectionCount(int[] y) {
+        final int n = y.length;
+        int ans = 0;
+        int intersectionCount = 0;
+        TreeMap<Integer, Integer> line = new TreeMap<>();
+
+        for (int i = 1; i < n; ++i) {
+            final int start = 2 * y[i - 1];
+            final int end = 2 * y[i] + (i == n - 1 ? 0 : y[i] > y[i - 1] ? -1 : 1);
+            line.merge(Math.min(start, end), 1, Integer::sum);
+            line.merge(Math.max(start, end) + 1, -1, Integer::sum);
+        }
+
+        for (final int count : line.values()) {
+            intersectionCount += count;
+            ans = Math.max(ans, intersectionCount);
+        }
+
+        return ans;
+    }
+}
 ```
 
 ```cpp

solution/3000-3099/3009.Maximum Number of Intersections on the Chart/README_EN.md

@@ -49,7 +49,28 @@
 ```
 
 ```java
-
+class Solution {
+    public int maxIntersectionCount(int[] y) {
+        final int n = y.length;
+        int ans = 0;
+        int intersectionCount = 0;
+        TreeMap<Integer, Integer> line = new TreeMap<>();
+
+        for (int i = 1; i < n; ++i) {
+            final int start = 2 * y[i - 1];
+            final int end = 2 * y[i] + (i == n - 1 ? 0 : y[i] > y[i - 1] ? -1 : 1);
+            line.merge(Math.min(start, end), 1, Integer::sum);
+            line.merge(Math.max(start, end) + 1, -1, Integer::sum);
+        }
+
+        for (final int count : line.values()) {
+            intersectionCount += count;
+            ans = Math.max(ans, intersectionCount);
+        }
+
+        return ans;
+    }
+}
 ```
 
 ```cpp

solution/3000-3099/3009.Maximum Number of Intersections on the Chart/Solution.java

@@ -0,0 +1,22 @@
+class Solution {
+    public int maxIntersectionCount(int[] y) {
+        final int n = y.length;
+        int ans = 0;
+        int intersectionCount = 0;
+        TreeMap<Integer, Integer> line = new TreeMap<>();
+
+        for (int i = 1; i < n; ++i) {
+            final int start = 2 * y[i - 1];
+            final int end = 2 * y[i] + (i == n - 1 ? 0 : y[i] > y[i - 1] ? -1 : 1);
+            line.merge(Math.min(start, end), 1, Integer::sum);
+            line.merge(Math.max(start, end) + 1, -1, Integer::sum);
+        }
+
+        for (final int count : line.values()) {
+            intersectionCount += count;
+            ans = Math.max(ans, intersectionCount);
+        }
+
+        return ans;
+    }
+}