Description

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.

Example:

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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.."]
]

Difficulty: Hard

Code:

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class Solution {
    public int totalNQueens(int n) {
        
    }
}

题意

N皇后问题，将n个皇后放在nxn的棋盘上，保证任意两个皇后不能相互攻击。

给定正整数n，求不重复的N皇后问题答案的个数。

Description

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.

Example:

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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.

Difficulty: Hard

Code:

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class Solution {
    public List<List<String>> solveNQueens(int n) {
        
    }
}

题意

N皇后问题，将n个皇后放在nxn的棋盘上，保证任意两个皇后不能相互攻击。

国际象棋中，皇后不仅能横竖走，还能走两个斜线。诞生八皇后问题，在一个8x8的棋盘上才能放8个皇后，保证不能相互攻击，即不能处于同一横线、竖线、斜线上。

给定正整数n，求不重复的N皇后问题答案。’Q’,’.’分别表示棋盘上的皇后和空格。

Description

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

Example 1:

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Input: 2.00000, 10
Output: 1024.00000

Example 2:

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Input: 2.10000, 3
Output: 9.26100

Example 3:

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Input: 2.00000, -2
Output: 0.25000
Explanation: 2-2 = 1/22 = 1/4 = 0.25

Note:

• -100.0 < x < 100.0
• n is a 32-bit signed integer, within the range [−231, 231 − 1]

Difficulty: Medium

Code:

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class Solution {
    public double myPow(double x, int n) {
        
    }
}

题意

求x的n次方，x范围是(-100.0, 100.0)，n是32位有符号整数其范围是[−231, 231 − 1]

Description

Given an array of strings, group anagrams together.

Example:

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

Note:

• All inputs will be in lowercase.
• The order of your output does not matter.

Difficulty: Medium

Code:

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class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        
    }
}

题意

给定一组字符串，按字谜（颠倒字母而成的字）分组。所有输入为小写，结果顺序不要求。

Description

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.

Example 1:

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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]
]

Example 2:

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Given input matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
], 

rotate the input matrix in-place such that it becomes:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]

Difficulty: Medium

Code:

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class Solution {
    public void rotate(int[][] matrix) {
        
    }
}

题意

给定一个n x n的二维矩阵表示一张图片，将图片顺时针旋转90度。要求直接修改二维矩阵，不允许使用额外的二维矩阵去做旋转。