题目描述

Implement the following operations of a stack using queues.

• push(x) — Push element x onto stack.
• pop() — Removes the element on top of the stack.
• top() — Get the top element.
• empty() — Return whether the stack is empty.

Example:

1
2
3
4
5
6
7

MyStack stack = new MyStack();

stack.push(1);
stack.push(2);  
stack.top();   // returns 2
stack.pop();   // returns 2
stack.empty(); // returns false

Notes:

• You must use only standard operations of a queue — which means only push to back, peek/pop from front, size, and is empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
• You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

题目描述

Given an input string (s) and a pattern (p), implement regular expression matching with support for '.' and '*'.

1
2

'.' Matches any single character.
'*' Matches zero or more of the preceding element.

The matching should cover the entire input string (not partial).

Note:

• s could be empty and contains only lowercase letters a-z.
• p could be empty and contains only lowercase letters a-z, and characters like . or *.

Example 1:

1
2
3
4
5

Input:
s = "aa"
p = "a"
Output: false
Explanation: "a" does not match the entire string "aa".

Example 2:

1
2
3
4
5

Input:
s = "aa"
p = "a*"
Output: true
Explanation: '*' means zero or more of the preceding element, 'a'. Therefore, by repeating 'a' once, it becomes "aa".

Example 3:

1
2
3
4
5

Input:
s = "ab"
p = ".*"
Output: true
Explanation: ".*" means "zero or more (*) of any character (.)".

Example 4:

1
2
3
4
5

Input:
s = "aab"
p = "c*a*b"
Output: true
Explanation: c can be repeated 0 times, a can be repeated 1 time. Therefore, it matches "aab".

Example 5:

1
2
3
4

Input:
s = "mississippi"
p = "mis*is*p*."
Output: false

题目描述

Implement a basic calculator to evaluate a simple expression string.

The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negativeintegers and empty spaces ``.

Example 1:

1
2

Input: "1 + 1"
Output: 2

Example 2:

1
2

Input: " 2-1 + 2 "
Output: 3

Example 3:

1
2

Input: "(1+(4+5+2)-3)+(6+8)"
Output: 23

Note:

• You may assume that the given expression is always valid.
• Do not use the eval built-in library function.

题目描述

Find the total area covered by two rectilinear rectangles in a 2D plane.

Each rectangle is defined by its bottom left corner and top right corner as shown in the figure.

Example:

1
2

Input: A = -3, B = 0, C = 3, D = 4, E = 0, F = -1, G = 9, H = 2
Output: 45

Note:

Assume that the total area is never beyond the maximum possible value of int.

题目描述

Given a complete binary tree, count the number of nodes.

Note:

Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

Example:

1
2
3
4
5
6
7
8

Input: 
    1
   / \
  2   3
 / \  /
4  5 6

Output: 6

题目描述

Given a 2D binary matrix filled with 0’s and 1’s, find the largest square containing only 1’s and return its area.

Example:

1
2
3
4
5
6
7
8

Input: 

1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0

Output: 4

题目描述

Given an array of integers, find out whether there are two distinct indices i and j in the array such that the absolutedifference between nums[i] and nums[j] is at most t and the absolute difference between i and j is at most k.

Example 1:

1
2

Input: nums = [1,2,3,1], k = 3, t = 0
Output: true

Example 2:

1
2

Input: nums = [1,0,1,1], k = 1, t = 2
Output: true

Example 3:

1
2

Input: nums = [1,5,9,1,5,9], k = 2, t = 3
Output: false

题目描述

Given a Weather table, write a SQL query to find all dates’ Ids with higher temperature compared to its previous (yesterday’s) dates.

1
2
3
4
5
6
7
8

+---------+------------------+------------------+
| Id(INT) | RecordDate(DATE) | Temperature(INT) |
+---------+------------------+------------------+
|       1 |       2015-01-01 |               10 |
|       2 |       2015-01-02 |               25 |
|       3 |       2015-01-03 |               20 |
|       4 |       2015-01-04 |               30 |
+---------+------------------+------------------+

For example, return the following Ids for the above Weather table:

1
2
3
4
5
6

+----+
| Id |
+----+
|  2 |
|  4 |
+----+

题目描述

Write a function that takes an unsigned integer and return the number of ‘1’ bits it has (also known as the Hamming weight).

Example 1:

1
2
3

Input: 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

Example 2:

1
2
3

Input: 00000000000000000000000010000000
Output: 1
Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.

Example 3:

1
2
3

Input: 11111111111111111111111111111101
Output: 31
Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.

题目描述

Reverse bits of a given 32 bits unsigned integer.

Example 1:

1
2

Input: 00000010100101000001111010011100
Output: 00111001011110000010100101000000

Example 2:

1
2

Input: 11111111111111111111111111111101
Output: 10111111111111111111111111111111