[pull] master from wisdompeak:master

DFS/3459.Length-of-Longest-V-Shaped-Diagonal-Segment/3459.Length-of-Longest-V-Shaped-Diagonal-Segment.cpp

@@ -0,0 +1,59 @@
+class Solution {
+    vector<pair<int,int>>dir;
+    int memo[501][501][4][2];
+public:
+    int lenOfVDiagonal(vector<vector<int>>& grid) 
+    {
+        int m = grid.size(), n = grid[0].size();
+        int ret = 0;
+        dir = {{-1,1},{1,1},{1,-1},{-1,-1}};
+
+        for (int i=0; i<m; i++)
+            for (int j=0; j<n; j++)
+            {
+                if (grid[i][j]==1)
+                {
+                    ret = max(ret, dfs(grid,i,j,0,1));
+                    ret = max(ret, dfs(grid,i,j,1,1));
+                    ret = max(ret, dfs(grid,i,j,2,1));
+                    ret = max(ret, dfs(grid,i,j,3,1));
+                }                    
+            }
+        return ret;
+    }
+
+    bool canContinue(int a, int b)
+    {
+        if (a==1 && b!=2) return false;
+        if (a==2 && b!=0) return false;
+        if (a==0 && b!=2) return false;
+        return true;
+    }
+    bool inbound(int i, int j, int m, int n)
+    {
+        return i>=0 && i<m && j>=0 && j<n;
+    }
+
+    int dfs(vector<vector<int>>& grid, int x, int y, int k, int t)
+    {        
+        if (memo[x][y][k][t]!=0) return memo[x][y][k][t];
+
+        int m = grid.size(), n = grid[0].size();
+        int ret = 1;
+
+        int i = x+dir[k].first, j = y+dir[k].second;
+
+        if (inbound(i,j,m,n) && canContinue(grid[x][y], grid[i][j]))
+            ret = max(ret, 1 + dfs(grid,i,j,k,t));
+
+        if (t==1)
+        {
+            int kk=(k+1)%4;
+            i = x+dir[k].first, j = y+dir[k].second;
+            if (inbound(i,j,m,n) && canContinue(grid[x][y], grid[i][j]))
+                ret = max(ret, 1 + dfs(grid,i,j,kk,0));        
+        }                
+        memo[x][y][k][t] = ret;
+        return ret;
+    }
+};

DFS/3459.Length-of-Longest-V-Shaped-Diagonal-Segment/Readme.md

@@ -0,0 +1,9 @@
+### 3459.Length-of-Longest-V-Shaped-Diagonal-Segment
+
+很常规的深度优先搜索。每个格子、每个方向只会进入一次。所以最多有`500*500*4=1e6`种状态。再加上有一次转弯的机会，所以2e6种状态是可以遍历和存储下来的。
+
+定义dfs(x,y,k,t)表示以k的方向进入(x,y)的格子、且还有t次转弯机会时，还能走的最长路径。如果t==0，那么只能按照k的方向进入下一个(i1,j1)；否则还可以考察按照k+1的方向进入下一个(i2,j2).
+
+注意进入的下一个各自(i,j)和(x,y)要满足数值上的约束，否则即可停止往下搜索。
+
+此外，本题的记忆化根据四个参数进行记忆化也是必须的。

Readme.md

@@ -552,6 +552,7 @@
 [2056.Number-of-Valid-Move-Combinations-On-Chessboard](https://github.com/wisdompeak/LeetCode/tree/master/DFS/2056.Number-of-Valid-Move-Combinations-On-Chessboard) (H)    
 [2065.Maximum-Path-Quality-of-a-Graph](https://github.com/wisdompeak/LeetCode/tree/master/DFS/2065.Maximum-Path-Quality-of-a-Graph) (M)      
 [2850.Minimum-Moves-to-Spread-Stones-Over-Grid](https://github.com/wisdompeak/LeetCode/tree/master/DFS/2850.Minimum-Moves-to-Spread-Stones-Over-Grid) (M)      
+[3459.Length-of-Longest-V-Shaped-Diagonal-Segment](https://github.com/wisdompeak/LeetCode/tree/master/DFS/3459.Length-of-Longest-V-Shaped-Diagonal-Segment) (M+)      
 * ``search in an array``    
 [090.Subsets-II](https://github.com/wisdompeak/LeetCode/tree/master/DFS/090.Subsets-II) (M+)  
 [301.Remove-Invalid-Parentheses](https://github.com/wisdompeak/LeetCode/tree/master/DFS/301.Remove-Invalid-Parentheses) (H)   
@@ -1478,7 +1479,7 @@
 [2781.Length-of-the-Longest-Valid-Substring](https://github.com/wisdompeak/LeetCode/tree/master/String/2781.Length-of-the-Longest-Valid-Substring) (H-)      
 [3394.Check-if-Grid-can-be-Cut-into-Sections](https://github.com/wisdompeak/LeetCode/tree/master/Greedy/3394.Check-if-Grid-can-be-Cut-into-Sections) (M)   
 [2271.Maximum-White-Tiles-Covered-by-a-Carpet](https://github.com/wisdompeak/LeetCode/tree/master/Greedy/2271.Maximum-White-Tiles-Covered-by-a-Carpet) (M+)       
-[3413.Maximum-Coins-From-K-Consecutive-Bags](https://github.com/wisdompeak/LeetCode/tree/master/Greedy/3413.Maximum-Coins-From-K-Consecutive-Bags) (H-)
+[3413.Maximum-Coins-From-K-Consecutive-Bags](https://github.com/wisdompeak/LeetCode/tree/master/Greedy/3413.Maximum-Coins-From-K-Consecutive-Bags) (H-)      
 3104.Find Longest Self-Contained Substring (TBD)      
 [1520.Maximum-Number-of-Non-Overlapping-Substrings](https://github.com/wisdompeak/LeetCode/tree/master/Greedy/1520.Maximum-Number-of-Non-Overlapping-Substrings) (H-)  
 [3458.Select-K-Disjoint-Special-Substrings](https://github.com/wisdompeak/LeetCode/tree/master/Greedy/3458.Select-K-Disjoint-Special-Substrings) (H-)