update cheatsheet topology_sorting.md

Author: yennanliu

doc/cheatsheet/topology_sorting.md

@@ -11,6 +11,8 @@
 ### 0-1) Types
 - Courses
     - LC 207, LC 210
+- Sequence
+    - LC 444
 - Alien Dictionary
     - LC 269
 
@@ -503,4 +505,73 @@ class Solution(object):
                 in_degree[word2[i]].add(word1[i])
                 out_degree[word1[i]].add(word2[i])
                 break　　
+```
+
+### 2-3) Sequence Reconstruction
+
+```java
+// java
+// LC 444
+    // V1
+    // https://www.youtube.com/watch?v=FHY1q1h9gq0
+    // https://www.jiakaobo.com/leetcode/444.%20Sequence%20Reconstruction.html
+    Map<Integer, Set<Integer>> map;
+    Map<Integer, Integer> indegree;
+
+    public boolean sequenceReconstruction_1(int[] nums, List<List<Integer>> sequences) {
+        map = new HashMap<>();
+        indegree = new HashMap<>();
+
+        for(List<Integer> seq: sequences) {
+            if(seq.size() == 1) {
+                addNode(seq.get(0));
+            } else {
+                for(int i = 0; i < seq.size() - 1; i++) {
+                    addNode(seq.get(i));
+                    addNode(seq.get(i + 1));
+
+                    // 加入子节点, 子节点增加一个入度
+                    // [1,2] => 1 -> 2
+                    // 1: [2]
+                    int curr = seq.get(i);
+                    int next = seq.get(i + 1);
+                    if(map.get(curr).add(next)) {
+                        indegree.put(next, indegree.get(next) + 1);
+                    }
+                }
+            }
+        }
+
+        Queue<Integer> queue = new LinkedList<>();
+        for(int key : indegree.keySet()) {
+            if(indegree.get(key) == 0){
+                queue.offer(key);
+            }
+        }
+
+        int index = 0;
+        while(!queue.isEmpty()) {
+            // 如果只有唯一解, 那么queue的大小永远都是1
+            if(queue.size() != 1) return false;
+
+            int curr = queue.poll();
+            if(curr != nums[index++]) return false;
+
+            for(int next: map.get(curr)) {
+                indegree.put(next, indegree.get(next) - 1);
+                if(indegree.get(next) == 0) {
+                    queue.offer(next);
+                }
+            }
+        }
+
+        return index == nums.length;
+    }
+
+    private void addNode(int node) {
+        if(!map.containsKey(node)) {
+            map.put(node, new HashSet<>());
+            indegree.put(node, 0);
+        }
+    }
 ```