a

Author: githubnotes

CF/algNotes/Breadth fitst search.md

@@ -58,44 +58,4 @@
 
 - Number of Islands (1 more)
 - Knight Shortest Path (to-do)
-- Build Post Office II (to-do)
-
-
-```java
-public class Solution {
-    /**
-     * @param root: the root of the given tree
-     * @return: the values of the nodes you can see ordered from top to bottom
-     */
-   
-  
-    public List<Integer> rightSideView(TreeNode root) {
-        // write your code here
-   List<Integer> res = ArrayList<>();
-        Queue <TreeNode> myQ = LinkedList<>();
-       
-        if(root == null){
-            return myQ;
-        }
-        
-        myQ.offer(root);
-        return helper();
-    }
-
-    public List<Integer> helper(){
-          List<Integer> res = ArrayList<>();
-        while(!myQ.isEmpty){
-            int size = myQ.size();
-
-            for(int i = 0; i < size; i++){
-                TreeNode node = myQ.poll();
-                res.add(node.val);
-                if(node.right != null){
-                      myQ.add(node.right);  
-                }
-            }
-        }
-        return res;
-    }
-}
-```
+- Build Post Office II (to-do)

CF/gp/gp1.md

@@ -59,4 +59,39 @@ Sum(i~j) = PrefixSum[j + 1] - PrefixSum[i]
     - 415. Valid Palindrome
 ## two pointer String
     - 637. valid Word Abbreviation
-    - 415. Valid Palindrome
+    - 415. Valid Palindrome
+
+
+
+# BFS类问题
+- 二叉树上的宽搜 BFS in Binary Tree
+- 图上的宽搜 BFS in Graph
+   - 拓扑排序 Topological Sorting
+- 棋盘上的宽搜 BFS
+
+- When should use BFS?
+- 图的遍历 Traversal in Graph
+  - 层级遍历 Level Order Traversal
+  - 由点及面 Connected Component
+  - 拓扑排序 Topological Sorting
+- 最短路径 Shortest Path in Simple Graph
+  - 仅限简单图求最短路径 
+    - (图中每条边，没有方向，没有权重)
+## BFS in Binary Tree
+    - Binary Tree Level Order Traversal
+    - Serialize and Deserialize Binary Tree (1 more)
+         - https://www.lintcode.com/help/binary-tree-representation/
+    - Binary Tree Level Order Traversal II
+    - Binary Tree Zigzag Order Traversal
+    - Convert Binary Tree to Linked Lists by Depth
+## BFS in graph (Undirected)
+    - 433. Number of Islands
+    - Knight Shortest Path (to-do)
+    - Build Post Office II (to-do)
+    - Clone graph
+        - find all nodes
+        - mapping old node to new node
+        - conncet all edges (copy neighbors)
+    - Graph Valid Tree
+## Minimum Spanning Tree
+    - 589. Connecting Graph

CF/gp/hf1.md

@@ -772,5 +772,49 @@ private Point global_origin = null;
             map.get(cur).add(pre);
         }
         return map;
-    } 
+    }
+
+
+
+
+public class Solution {
+    /**
+     * @param grid: a boolean 2D matrix
+     * @return: an integer
+     */
+    public int numIslands(boolean[][] grid) {
+        // write your code here
+        if(grid == null || grid.length == 0){
+            return 0;
+        }
+        
+        int m = grid.length;
+        System.out.println(m);
+        int n = grid[0].length;
+        System.out.println(n);
+         int res = 0;
+        
+        for(int i = 0; i < m; i++){
+            for(int j = 0; j < n; j++){
+                if(grid[i][j]){
+                    dfs(grid, i,j,m,n);
+                    res++;
+                }
+            }
+        }
+        
+        return res;
+    }
+    
+    private void dfs(boolean[][] grid,int x, int y, int m,int n){
+        if(x >= m || y >= n || x < 0|| y < 0 || !grid[x][y]){
+            return;
+        }
+        grid[x][y] = false;
+        dfs(grid,x-1,y,m,n);
+        dfs(grid,x+1,y,m,n);
+        dfs(grid,x,y-1,m,n);
+        dfs(grid,x,y+1,m,n);
+    }
+}
 ```