java: add «3203. Find Minimum Diameter After Merging Two Trees»

URL:	https://leetcode.com/problems/find-minimum-diameter-after-merging-two-trees/

java/find-minimum-diameter-after-merging-two-trees.java

@@ -0,0 +1,65 @@
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.List;
+
+class Solution {
+  private List<List<Integer>> makeGraph(int[][] edges) {
+    var n = edges.length + 1;
+
+    var g = new ArrayList<List<Integer>>();
+    for (int i = 0; i < n; ++i) {
+      g.add(new ArrayList<>());
+    }
+
+    for (var edge : edges) {
+      g.get(edge[0]).add(edge[1]);
+      g.get(edge[1]).add(edge[0]);
+    }
+
+    return g;
+  }
+
+  private int getDiameter(int[][] edges) {
+    var n = edges.length + 1;
+    var g = makeGraph(edges);
+    var deg = new int[n];
+
+    var q = new ArrayDeque<Integer>();
+    for (int i = 0; i < n; ++i) {
+      deg[i] = g.get(i).size();
+      if (deg[i] == 1) {
+        q.offer(i);
+      }
+    }
+
+    int levelsRemoved = 0;
+
+    int remaining = n;
+    while (remaining > 2) {
+      var size = q.size();
+      remaining -= size;
+      ++levelsRemoved;
+
+      for (int i = 0; i < size; ++i) {
+        var u = q.poll();
+
+        for (var v : g.get(u)) {
+          --deg[v];
+          if (deg[v] == 1) {
+            q.offer(v);
+          }
+        }
+      }
+    }
+
+    return 2 * levelsRemoved + ((remaining == 2) ? 1 : 0);
+  }
+
+  public int minimumDiameterAfterMerge(int[][] edges1, int[][] edges2) {
+    var d1 = getDiameter(edges1);
+    var d2 = getDiameter(edges2);
+    var combined = (d1 / 2 + d1 % 2) + (d2 / 2 + d2 % 2) + 1;
+
+    return Math.max(combined, Math.max(d1, d2));
+  }
+}