Bright's Blog

Description

Difficulty: Hard

Given a 2D array of characters grid of size m x n, you need to find if there exists any cycle consisting of the same value in grid.

A cycle is a path of length 4 or more in the grid that starts and ends at the same cell. From a given cell, you can move to one of the cells adjacent to it in one of the four directions (up, down, left, or right), if it has the same value of the current cell.

Also, you cannot move to the cell that you visited in your last move. For example, the cycle (1, 1) -> (1, 2) -> (1, 1) is invalid because from (1, 2) we visited (1, 1) which was the last visited cell.

Return true if any cycle of the same value exists in grid, otherwise, return false.

Example 1:

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Input: grid = [ ["a","a","a","a"], ["a","b","b","a"], ["a","b","b","a"], ["a","a","a","a"] ] Output: true Explanation: There are two valid cycles。

Example 2:

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Input: grid = [ ["c","c","c","a"], ["c","d","c","c"], ["c","c","e","c"], ["f","c","c","c"] ] Output: true Explanation: There is only one valid cycle highlighted in the image below:

Example 3:

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Input: grid = [ ["a","b","b"], ["b","z","b"], ["b","b","a"] ] Output: false

Constraints:

m == grid.length
n == grid[i].length
1 <= m <= 500
1 <= n <= 500
grid consists only of lowercase English letters.

前言

「 Leetcode 系列题解 」 (持续更新中，目前专注于剑指offer系列)

Description

Difficulty: Medium

Given a 2D board and a word, find if the word exists in the grid.

The word can be constructed from letters of sequentially adjacent cell, where “adjacent” cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.

Example:

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board = [ ['A','B','C','E'], ['S','F','C','S'], ['A','D','E','E'] ] Given word = "ABCCED", return true. Given word = "SEE", return true. Given word = "ABCB", return false.

Description

Difficulty: Simple

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

(i.e., [0,1,2,4,5,6,7] might become [4,5,6,7,0,1,2]).

Find the minimum element.

The array may contain duplicates.

Example 1:

1 2	Input: [1,3,5] Output: 1

Example 2:

1 2	Input: [2,2,2,0,1] Output: 0

Description

Difficulty: Simple

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

Example 1:

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Input: 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps

Example 2:

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Input: 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step

Constraint：

0 <= n <= 45

Description

Difficulty: Simple

The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,

1 2	F(0) = 0, F(1) = 1 F(N) = F(N - 1) + F(N - 2), for N > 1.

Given N, calculate F(N).

答案需要取模 1e9+7（1000000007），如计算初始结果为：1000000008，请返回 1。

Example:

1 2 3

Input: 4 >Output: 3 >Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.