LeetCode 92. Reverse Linked List II [Medium] [C++] 解題筆記

Reverse a linked list from position m to n. Do it in one-pass.

Note: 1 ≤ m ≤ n ≤ length of list.

EX:

        Input: 1->2->3->4->5->NULL, m = 2, n = 4

        Output: 1->4->3->2->5->NULL

LeetCode 53. Maximum Subarray [Easy] [C++] 解題筆記

Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.

EX:

        Input: [-2,1,-3,4,-1,2,1,-5,4],

        Output: 6
Explanation: [4,-1,2,1] has the largest sum = 6.

LeetCode 52. N-Queens II [Hard] [C++] 解題筆記

The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.

Given an integer n, return the number of distinct solutions to the n-queens puzzle.

EX:

     Input: 4

    Output: 2
    Explanation: There are two distinct solutions to the 4-queens puzzle as shown below.
    [
     [".Q..",  // Solution 1
      "...Q",
      "Q...",
      "..Q."],

     ["..Q.",  // Solution 2
      "Q...",
      "...Q",
      ".Q.."]
    ]

LeetCode 51. N-Queens [Hard] [C++] 解題筆記

這題是經典的 n 皇后問題。

The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle.

Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space respectively.

EX:

        Input: 4

        Output: [
         [".Q..",  // Solution 1
          "...Q",
          "Q...",
          "..Q."],

         ["..Q.",  // Solution 2
          "Q...",
          "...Q",
          ".Q.."]
        ]
Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above.

LeetCode 50. Pow(x, n) [Medium] [C++] 解題筆記

Implement pow(x, n), which calculates x raised to the power n (xⁿ).

EX:

        Input: 2.00000, 10

        Output: 1024.00000

        Input: 2.00000, -2

        Output: 0.25000
        Explanation: 2-2 = 1/22 = 1/4 = 0.25

LeetCode 49. Group Anagrams [Medium] [C++] 解題筆記

這題給定一個 array 包含一些 string，要求我們將由同樣字元組成的 string 歸到同一個 array。

EX:

        Input: ["eat", "tea", "tan", "ate", "nat", "bat"],

        Output:
        [
          ["ate","eat","tea"],
          ["nat","tan"],
          ["bat"]
        ]

LeetCode 48. Rotate Image [Medium] [C++] 解題筆記

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Note:

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

EX:

        Given input matrix = 

    [
      [1,2,3],
      [4,5,6],
      [7,8,9]
    ],

    rotate the input matrix in-place such that it becomes:
    [
      [7,4,1],
      [8,5,2],
      [9,6,3]
    ]

LeetCode 47. Permutations II [Medium] [C++] 解題筆記

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

EX:

        Input: [1,1,2]

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

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]
    ]