modify code

Author: algorithmzuo

src/topinterviewquestions/Problem_0687_LongestUnivaluePath.java

@@ -0,0 +1,56 @@
+package topinterviewquestions;
+
+public class Problem_0687_LongestUnivaluePath {
+
+	public static class TreeNode {
+		public int val;
+		public TreeNode left;
+		public TreeNode right;
+
+		public TreeNode(int v) {
+			val = v;
+		}
+	}
+
+	public static int longestUnivaluePath(TreeNode root) {
+		if (root == null) {
+			return 0;
+		}
+		return process(root).max - 1;
+	}
+
+	// 建设以x节点为头的树，返回两个信息
+	public static class Info {
+		// 在一条路径上：要求每个节点通过且只通过一遍
+		public int len; // 路径必须从x出发且只能往下走的情况下，路径的最大距离
+		public int max; // 路径不要求必须从x出发的情况下，整棵树的合法路径最大距离
+
+		public Info(int l, int m) {
+			len = l;
+			max = m;
+		}
+	}
+
+	private static Info process(TreeNode x) {
+		if (x == null) {
+			return new Info(0, 0);
+		}
+		TreeNode l = x.left;
+		TreeNode r = x.right;
+		Info linfo = process(l);
+		Info rinfo = process(r);
+		int len = 1;
+		if (l != null && l.val == x.val) {
+			len = linfo.len + 1;
+		}
+		if (r != null && r.val == x.val) {
+			len = Math.max(len, rinfo.len + 1);
+		}
+		int max = Math.max(Math.max(linfo.max, rinfo.max), len);
+		if (l != null && r != null && l.val == x.val && r.val == x.val) {
+			max = Math.max(max, linfo.len + rinfo.len + 1);
+		}
+		return new Info(len, max);
+	}
+
+}