LeetCode 46. Permutations [Medium] [C++] 解題筆記

Given a collection of distinct integers, return all possible permutations.

EX:

        Input: [1,2,3]

    Output:
    [
      [1,2,3],
      [1,3,2],
      [2,1,3],
      [2,3,1],
      [3,1,2],
      [3,2,1]
    ]

LeetCode 44. Wildcard Matching [Hard] [C++] 解題筆記

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

'?' Matches any single character.
'*' Matches any sequence of characters (including the empty sequence).

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 *.

注意這裡的 '*' 是匹配任意字串!

EX:

    Input:

    s = "adceb"
    p = "*a*b"
    Output: true
    Explanation: The first '*' matches the empty sequence, while the second '*' matches the substring "dce".

LeetCode 43. Multiply Strings [Medium] [C++] 解題筆記

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

EX:

        Input: num1 = "123", num2 = "456"

        Output: "56088"

LeetCode 41. First Missing Positive [Hard] [C++] 解題筆記

Given an unsorted integer array, find the smallest missing positive integer.

EX:

        Input: [1,2,0]

        Output: 3

        Input: [3,4,-1,1]

        Output: 2

        Input: [7,8,9,11,12]

        Output: 1

LeetCode 40. Combination Sum II [Medium] [C++] 解題筆記

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

Each number in candidates may only be used once in the combination.

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

EX:

        Input: candidates = [10,1,2,7,6,1,5], target = 8,

    A solution set is:
    [
      [1, 7],
      [1, 2, 5],
      [2, 6],
      [1, 1, 6]
    ]

LeetCode 39. Combination Sum [Medium] [C++] 解題筆記

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

The same repeated number may be chosen from candidates unlimited number of times.

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

EX:

        Input: candidates = [2,3,5], target = 8,

    A solution set is:
    [
      [2,2,2,2],
      [2,3,3],
      [3,5]
    ]

LeetCode 38. Count and Say [Easy] [C++] 解題筆記

The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     1
2.     11
3.     21
4.     1211
5.     111221

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.

Given an integer n where 1 ≤ n ≤ 30, generate the n^th term of the count-and-say sequence. You can do so recursively, in other words from the previous member read off the digits, counting the number of digits in groups of the same digit.

Note: Each term of the sequence of integers will be represented as a string.

EX:

        Input: 4

        Output: "1211"

Explanation: For n = 3 the term was "21" in which we have two groups "2" and "1", "2" can be read as "12" 

which means frequency = 1 and value = 2, 

the same way "1" is read as "11", so the answer is the concatenation of "12" and "11" which is "1211".

LeetCode 37. Sudoku Solver [Hard] [C++] 解題筆記

這題是 36. Valid Sudoku 的進階題，要我們實作一個 9 X 9 數獨的 Solver。

EX:

                                    

LeetCode 36. Valid Sudoku [Medium] [C++] 解題筆記

這題給我們一個玩到一半的 9 X 9 數獨，要我們判斷目前的結果是不是正確的(有沒有符合數獨的規定)。

EX:

        Input:

[
  ["5","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
    Output: true

LeetCode 35. Search Insert Position [Easy] [C++] 解題筆記

Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.

You may assume no duplicates in the array.

EX:

        Input: [1,3,5,6], 5

        Output: 2

LeetCode 34. Find First and Last Position of Element in Sorted Array [Medium] [C++] 解題筆記

Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.

Your algorithm's runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

EX:

        Input: nums = [5,7,7,8,8,10], target = 8

        Output: [3,4]

        Input: nums = [5,7,7,8,8,10], target = 6

        Output: [-1,-1]

LeetCode 32. Longest Valid Parentheses [Hard] [C++] 解題筆記

Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

EX:

        Input: "(()"

        Output: 2

        Explanation: The longest valid parentheses substring is "()"

        Input: ")()())"

        Output: 4

        Explanation: The longest valid parentheses substring is "()()"

LeetCode 31. Next Permutation [Medium] [C++] 解題筆記

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place and use only constant extra memory.

EX:

        1,2,3 → 1,3,2

    3,2,1 → 1,2,3

    1,1,5 → 1,5,1