Matrix

Problem Suppose you are at a party with n people (labeled from 0 to n - 1) and among them, there may exist one celebrity. The definition of a celebrity is that all the other n - 1 people know him/her but he/she does not know any of them. Now you want to find out who the celebrity is or verify that there is not one. The only thing you are allowed to do is to ask questions like: “Hi, A. Do you know B?” to get information of whether A knows B. You need to find out the celebrity (or verify there is not one) by asking as few questions as possible (in the asymptotic sense). ...

Transpose a Matrix Problem Given a 2D integer array matrix, return the transpose of matrix. The transpose of a matrix is the matrix flipped over its main diagonal, switching the matrix’s row and column indices. Example Example 1: $$ \begin{bmatrix} \colorbox{red} 1 & \colorbox{red} 2 & \colorbox{red}3 \\ \colorbox{green} 4 & \colorbox{green} 5 & \colorbox{green}6 \\ \colorbox{blue} 7 & \colorbox{blue} 8 & \colorbox{blue}9 \end{bmatrix} \Longrightarrow \begin{bmatrix} \colorbox{red} 1 & \colorbox{green} 4 & \colorbox{blue} 7 \\ \colorbox{red} 2 & \colorbox{green} 5 & \colorbox{blue} 8 \\ \colorbox{red} 3 & \colorbox{green} 6 & \colorbox{blue} 9 \end{bmatrix} $$ ...

Problem There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right or diagonally at any point in time. Given the two integers m and n, return the number of possible unique paths that the robot can take to reach the bottom-right corner. ...

Problem There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n, return the number of possible unique paths that the robot can take to reach the bottom-right corner. ...

Problem Given an m x n matrix of 0s and 1s, provide an algorithm such that if an element is 0, its entire row and column is set to 0 OR Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0’s. You must do it in place. Follow Up: Can you do it in one pass? ...

Problem An image is represented by an m x n integer grid image where image[i][j] represents the pixel value of the image. You are also given three integers sr, sc, and color. You should perform a flood fill on the image starting from the pixel image[sr][sc]. To perform a flood fill, consider the starting pixel, plus any pixels connected 4-directionally to the starting pixel of the same color as the starting pixel, plus any pixels connected 4-directionally to those pixels (also with the same color), and so on. Replace the color of all of the aforementioned pixels with color. ...

Problem Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Examples Example 1: Input: grid = [ ["1","1","1","1","0"], ["1","1","0","1","0"], ["1","1","0","0","0"], ["0","0","0","0","0"] ] Output: 1 ...

Problem You are given an m x n integer array grid. There is a robot initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m-1][n-1]). The robot can only move either down or right at any point in time. An obstacle and space are marked as 1 or 0 respectively in grid. A path that the robot takes cannot include any square that is an obstacle. ...

Problem Given a positive integer n, generate an n x n matrix filled with elements from 1 to n2 in spiral order. Examples Example 1: Input: n = 3 Output: [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ] Example 2: Input: n = 4 Output: [ [1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7] ] ...

Problem Given a 2D grid of size m x n and an integer k. You need to shift the grid k times. In one shift operation: Element at grid[i][j] moves to grid[i][j + 1]. Element at grid[i][n - 1] moves to grid[i + 1][0]. Element at grid[m - 1][n - 1] moves to grid[0][0]. Return the 2D grid after applying shift operation k times. Examples Example 1: ...