leetcode Counting Bits
Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1’s in their binary representation and return them as an array.
num = 5you should return
- It is very easy to come up with a solution with run time O(n*sizeof(integer)). But can you do it in linear time O(n) /possibly in a single pass?
- Space complexity should be O(n).
- Can you do it like a boss? Do it without using any builtin function like __builtin_popcount in c++ or in any other language.
leetcode House Robber III
The thief has found himself a new place for his thievery again. There is only one entrance to this area, called the “root.” Besides the root, each house has one and only one parent house. After a tour, the smart thief realized that “all houses in this place forms a binary tree”. It will automatically contact the police if two directly-linked houses were broken into on the same night.
Determine the maximum amount of money the thief can rob tonight without alerting the police.
12345 3/ \2 3\ \3 1
Maximum amount of money the thief can rob = 3 + 3 + 1 = 7.
12345 3/ \4 5/ \ \1 3 1
Maximum amount of money the thief can rob = 4 + 5 = 9.
leetcode Self Crossing
You are given an array x of
npositive numbers. You start at point
xmetres to the north, then
xmetres to the west,
xmetres to the south,
xmetres to the east and so on. In other words, after each move your direction changes counter-clockwise.
Write a one-pass algorithm with
O(1)extra space to determine, if your path crosses itself, or not.
Given x =
[2, 1, 1, 2]
Given x =
[1, 2, 3, 4]
false(not self crossing)
Given x =
[1, 1, 1, 1]
leetcode Increasing Triplet Subsequence
Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.
Formally the function should:
Return true if there exists i, j, k
such that arr[i] < arr[j] < arr[k] given 0 ≤ i < j < k ≤ n-1 else return false.Your algorithm should run in O(n) time complexity and O(1) space complexity.
[1, 2, 3, 4, 5],
[5, 4, 3, 2, 1],
leetcode Reconstruct Itinerary
Given a list of airline tickets represented by pairs of departure and arrival airports
[from, to], reconstruct the itinerary in order. All of the tickets belong to a man who departs from
JFK. Thus, the itinerary must begin with
- If there are multiple valid itineraries, you should return the itinerary that has the smallest lexical order when read as a single string. For example, the itinerary
["JFK", "LGA"]has a smaller lexical order than
- All airports are represented by three capital letters (IATA code).
- You may assume all tickets may form at least one valid itinerary.
[["MUC", "LHR"], ["JFK", "MUC"], ["SFO", "SJC"], ["LHR", "SFO"]]
["JFK", "MUC", "LHR", "SFO", "SJC"].
Another possible reconstruction is
["JFK","SFO","ATL","JFK","ATL","SFO"]. But it is larger in lexical order.
leetcode Verify Preorder Serialization of a Binary Tree
One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node’s value. If it is a null node, we record using a sentinel value such as
1234567 _9_/ \3 2/ \ / \4 1 # 6/ \ / \ / \# # # # # #
For example, the above binary tree can be serialized to the string
#represents a null node.
Given a string of comma separated values, verify whether it is a correct preorder traversal serialization of a binary tree. Find an algorithm without reconstructing the tree.
Each comma separated value in the string must be either an integer or a character
You may assume that the input format is always valid, for example it could never contain two consecutive commas such as
leetcode Patching Array
Given a sorted positive integer array nums and an integer n, add/patch elements to the array such that any number in range
[1, n]inclusive can be formed by the sum of some elements in the array. Return the minimum number of patches required.
[1, 3], n =
Combinations of nums are
, , [1,3], which form possible sums of:
1, 3, 4.
Now if we add/patch
2to nums, the combinations are:
, , , [1,3], [2,3], [1,2,3].
Possible sums are
1, 2, 3, 4, 5, 6, which now covers the range
So we only need
leetcode Longest Increasing Path in a Matrix
Given an integer matrix, find the length of the longest increasing path.
From each cell, you can either move to four directions: left, right, up or down. You may NOT move diagonally or move outside of the boundary (i.e. wrap-around is not allowed).
nums = [
The longest increasing path is
[1, 2, 6, 9].
leetcode Odd Even Linked List
Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.
You should try to do it in place. The program should run in O(1) space complexity and O(nodes) time complexity.
The relative order inside both the even and odd groups should remain as it was in the input.
The first node is considered odd, the second node even and so on …
leetcode Count of Range Sum
Given an integer array
nums, return the number of range sums that lie in
S(i, j)is defined as the sum of the elements in
A naive algorithm of O(n2) is trivial. You MUST do better than that.
Given nums =
[-2, 5, -1], lower =
-2, upper =
The three ranges are :
[0, 2]and their respective sums are:
-2, -1, 2.