diff --git a/src/main/java/leetcode/editor/cn/RedundantConnection.java b/src/main/java/leetcode/editor/cn/RedundantConnection.java
new file mode 100644
index 0000000..e1650eb
--- /dev/null
+++ b/src/main/java/leetcode/editor/cn/RedundantConnection.java
@@ -0,0 +1,112 @@
+//<p>树可以看成是一个连通且 <strong>无环&nbsp;</strong>的&nbsp;<strong>无向&nbsp;</strong>图。</p>
+//
+//<p>给定往一棵&nbsp;<code>n</code> 个节点 (节点值&nbsp;<code>1～n</code>) 的树中添加一条边后的图。添加的边的两个顶点包含在 <code>1</code> 到 <code>n</code>&nbsp;中间，且这条附加的边不属于树中已存在的边。图的信息记录于长度为 <code>n</code> 的二维数组 <code>edges</code>&nbsp;，<code>edges[i] = [a<sub>i</sub>, b<sub>i</sub>]</code>&nbsp;表示图中在 <code>ai</code> 和 <code>bi</code> 之间存在一条边。</p>
+//
+//<p>请找出一条可以删去的边，删除后可使得剩余部分是一个有着 <code>n</code> 个节点的树。如果有多个答案，则返回数组&nbsp;<code>edges</code>&nbsp;中最后出现的边。</p>
+//
+//<p>&nbsp;</p>
+//
+//<p><strong>示例 1：</strong></p>
+//
+//<p><img alt="" src="https://pic.leetcode-cn.com/1626676174-hOEVUL-image.png" style="width: 152px; " /></p>
+//
+//<pre>
+//<strong>输入:</strong> edges = [[1,2], [1,3], [2,3]]
+//<strong>输出:</strong> [2,3]
+//</pre>
+//
+//<p><strong>示例 2：</strong></p>
+//
+//<p><img alt="" src="https://pic.leetcode-cn.com/1626676179-kGxcmu-image.png" style="width: 250px; " /></p>
+//
+//<pre>
+//<strong>输入:</strong> edges = [[1,2], [2,3], [3,4], [1,4], [1,5]]
+//<strong>输出:</strong> [1,4]
+//</pre>
+//
+//<p>&nbsp;</p>
+//
+//<p><strong>提示:</strong></p>
+//
+//<ul> 
+// <li><code>n == edges.length</code></li> 
+// <li><code>3 &lt;= n &lt;= 1000</code></li> 
+// <li><code>edges[i].length == 2</code></li> 
+// <li><code>1 &lt;= ai&nbsp;&lt; bi&nbsp;&lt;= edges.length</code></li> 
+// <li><code>ai != bi</code></li> 
+// <li><code>edges</code> 中无重复元素</li> 
+// <li>给定的图是连通的&nbsp;</li> 
+//</ul>
+//
+//<div><div>Related Topics</div><div><li>深度优先搜索</li><li>广度优先搜索</li><li>并查集</li><li>图</li></div></div><br><div><li>👍 523</li><li>👎 0</li></div>
+package leetcode.editor.cn;
+
+import java.util.*;
+
+// 684:冗余连接
+public class RedundantConnection {
+    public static void main(String[] args) {
+        Solution solution = new RedundantConnection().new Solution();
+        // TO TEST
+    }
+
+    //leetcode submit region begin(Prohibit modification and deletion)
+    class Solution {
+        public int[] findRedundantConnection(int[][] edges) {
+            List<List<Integer>> list = new ArrayList<>();
+            for (int[] edge : edges) {
+                if (list.size() == 0) {
+                    list.add(new ArrayList<>(Arrays.asList(edge[0], edge[1])));
+                } else {
+                    int index0 = -1;
+                    int index1 = -1;
+                    for (int i = list.size() - 1; i >= 0; i--) {
+                        if (list.get(i).contains(edge[0])) {
+                            index0 = i;
+                            if (index1 > -1) {
+                                break;
+                            }
+                        }
+                        if (list.get(i).contains(edge[1])) {
+                            index1 = i;
+                            if (index0 > -1) {
+                                break;
+                            }
+                        }
+                    }
+                    if (index0 > -1 && index0 == index1) {
+                        return edge;
+                    }
+                    Set<Integer> tmp = new HashSet<>();
+                    if (index0 > -1) {
+                        tmp.addAll(list.get(index0));
+                    } else {
+                        tmp.add(edge[0]);
+                    }
+                    if (index1 > -1) {
+                        tmp.addAll(list.get(index1));
+                    } else {
+                        tmp.add(edge[1]);
+                    }
+                    if (index0 > -1 && index1 > -1) {
+                        if (index0 > index1) {
+                            list.remove(index0);
+                            list.remove(index1);
+                        } else {
+                            list.remove(index1);
+                            list.remove(index0);
+                        }
+                    } else if (index0 > -1) {
+                        list.remove(index0);
+                    } else if (index1 > -1) {
+                        list.remove(index1);
+                    }
+                    list.add(new ArrayList<>(tmp));
+                }
+            }
+            return null;
+        }
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}
diff --git a/src/main/java/leetcode/editor/cn/doc/content/RedundantConnection.md b/src/main/java/leetcode/editor/cn/doc/content/RedundantConnection.md
new file mode 100644
index 0000000..40f5c48
--- /dev/null
+++ b/src/main/java/leetcode/editor/cn/doc/content/RedundantConnection.md
@@ -0,0 +1,41 @@
+<p>树可以看成是一个连通且 <strong>无环&nbsp;</strong>的&nbsp;<strong>无向&nbsp;</strong>图。</p>
+
+<p>给定往一棵&nbsp;<code>n</code> 个节点 (节点值&nbsp;<code>1～n</code>) 的树中添加一条边后的图。添加的边的两个顶点包含在 <code>1</code> 到 <code>n</code>&nbsp;中间，且这条附加的边不属于树中已存在的边。图的信息记录于长度为 <code>n</code> 的二维数组 <code>edges</code>&nbsp;，<code>edges[i] = [a<sub>i</sub>, b<sub>i</sub>]</code>&nbsp;表示图中在 <code>ai</code> 和 <code>bi</code> 之间存在一条边。</p>
+
+<p>请找出一条可以删去的边，删除后可使得剩余部分是一个有着 <code>n</code> 个节点的树。如果有多个答案，则返回数组&nbsp;<code>edges</code>&nbsp;中最后出现的边。</p>
+
+<p>&nbsp;</p>
+
+<p><strong>示例 1：</strong></p>
+
+<p><img alt="" src="https://pic.leetcode-cn.com/1626676174-hOEVUL-image.png" style="width: 152px; " /></p>
+
+<pre>
+<strong>输入:</strong> edges = [[1,2], [1,3], [2,3]]
+<strong>输出:</strong> [2,3]
+</pre>
+
+<p><strong>示例 2：</strong></p>
+
+<p><img alt="" src="https://pic.leetcode-cn.com/1626676179-kGxcmu-image.png" style="width: 250px; " /></p>
+
+<pre>
+<strong>输入:</strong> edges = [[1,2], [2,3], [3,4], [1,4], [1,5]]
+<strong>输出:</strong> [1,4]
+</pre>
+
+<p>&nbsp;</p>
+
+<p><strong>提示:</strong></p>
+
+<ul> 
+ <li><code>n == edges.length</code></li> 
+ <li><code>3 &lt;= n &lt;= 1000</code></li> 
+ <li><code>edges[i].length == 2</code></li> 
+ <li><code>1 &lt;= ai&nbsp;&lt; bi&nbsp;&lt;= edges.length</code></li> 
+ <li><code>ai != bi</code></li> 
+ <li><code>edges</code> 中无重复元素</li> 
+ <li>给定的图是连通的&nbsp;</li> 
+</ul>
+
+<div><div>Related Topics</div><div><li>深度优先搜索</li><li>广度优先搜索</li><li>并查集</li><li>图</li></div></div><br><div><li>👍 523</li><li>👎 0</li></div>
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