.

Author: hqztrue

1201-1300/1293. Shortest Path in a Grid with Obstacles Elimination.txt

@@ -1,4 +1,4 @@
 dijkstra (bfs). O(nm*min(k,n+m)), because we can wlog assume k<=n+m.
 
-remark. this is a special case (unweighted, planar) of the bicriteria s,t-path problem.
+remark. this is a special case (unweighted, planar) of the bicriteria s,t-path problem. Maybe we can prove some lower bound?
 

1601-1700/1660. Correct a Binary Tree.txt

@@ -0,0 +1,2 @@
+compute the level of each node. O(n).
+

1601-1700/1666. Change the Root of a Binary Tree.txt

@@ -0,0 +1,2 @@
+O(n) or O(h).
+

1601-1700/1668. Maximum Repeating Substring.txt

@@ -0,0 +1,2 @@
+kmp, find all occurrences of word. O(n).
+

1601-1700/1669. Merge In Between Linked Lists.txt

@@ -0,0 +1,2 @@
+O(n).
+

1601-1700/1670. Design Front Middle Back Queue.txt

@@ -0,0 +1,2 @@
+linked list. O(1) per operation.
+

1601-1700/1671. Minimum Number of Removals to Make Mountain Array.txt

@@ -0,0 +1,2 @@
+LIS. O(n log n).
+

1601-1700/1676. Lowest Common Ancestor of a Binary Tree IV.txt

@@ -0,0 +1,2 @@
+O(n).
+

1601-1700/1679. Max Number of K-Sum Pairs.txt

@@ -0,0 +1,2 @@
+hashing. O(n).
+

1601-1700/1680. Concatenation of Consecutive Binary Numbers.txt

@@ -0,0 +1,4 @@
+We can easily compute the concatenation of 2^i...2^{i+1}-1 using math formula. O(log^2 n). (the bottleneck is computing (2^i-1)^{-1} mod P)
+
+https://stackoverflow.com/questions/64450456/concatenation-of-binary-representation-of-first-n-positive-integers-in-ologn-t
+

README.md

@@ -44,7 +44,7 @@ Problem ID marked with leading ~ indicates there's good evidences that the algor
 ~898 Bitwise ORs of Subarrays  
 1057 Campus Bikes  
 ~1074 Number of Submatrices That Sum to Target  
-1293 Shortest Path in a Grid with Obstacles Elimination  
+~1293 Shortest Path in a Grid with Obstacles Elimination  
 1316 Distinct Echo Substrings  
 ~1334 Find the City With the Smallest Number of Neighbors at a Threshold Distance  
 ~1335 Minimum Difficulty of a Job Schedule