Pretty Sure

LeetCode - Maximum Swap

Question Definition

Given a non-negative integer, you could swap two digits at most once to get the maximum valued number. Return the maximum valued number you could get.

LeetCode - Insert Delete GetRandom O(1)

Question Definition

Design a data structure that supports all following operations in average O(1) time.

1. insert(val): Inserts an item val to the set if not already present.
2. remove(val): Removes an item val from the set if present.
3. getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.

LeetCode - Game of Life

Question Definition

According to the Wikipedia’s article: “The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway in 1970.”

Given a board with m by n cells, each cell has an initial state live (1) or dead (0). Each cell interacts with its eight neighbors (horizontal, vertical, diagonal) using the following four rules (taken from the above Wikipedia article):

1. Any live cell with fewer than two live neighbors dies, as if caused by under-population.
2. Any live cell with two or three live neighbors lives on to the next generation.
3. Any live cell with more than three live neighbors dies, as if by over-population..
4. Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction. Write a function to compute the next state (after one update) of the board given its current state.

**Follow up: **

1. Could you solve it in-place? Remember that the board needs to be updated at the same time: You cannot update some cells first and then use their updated values to update other cells.
2. In this question, we represent the board using a 2D array. In principle, the board is infinite, which would cause problems when the active area encroaches the border of the array. How would you address these problems?

My Java Solution

public void gameOfLife(int[][] board) {
    for(int i = 0; i < board.length; i++){
        for(int j = 0; j < board[i].length; j++){
            int neighbors = 0;
            if(i > 0 && Math.abs(board[i - 1][j]) == 1)
                neighbors++;
            if(j > 0 && Math.abs(board[i][j - 1]) == 1)
                neighbors++;
            if(i > 0 && j > 0 && Math.abs(board[i - 1][j - 1]) == 1)
                neighbors++;
            if(i > 0 && j < board[i].length - 1 && Math.abs(board[i - 1][j + 1]) == 1)
                neighbors++;
            if(j < board[i].length - 1 && Math.abs(board[i][j + 1]) == 1)
                neighbors++;
            if(i < board.length - 1 && j < board[i].length - 1 && Math.abs(board[i + 1][j + 1]) == 1)
                neighbors++;
            if(i < board.length - 1 && j > 0 && Math.abs(board[i + 1][j - 1]) == 1)
                neighbors++;
            if(i < board.length - 1 && Math.abs(board[i + 1][j]) == 1)
                neighbors++;
            if(Math.abs(board[i][j]) == 1){
                if(neighbors < 2 || neighbors > 3)
                    board[i][j] = -1;
            } else {
                if(neighbors == 3)
                    board[i][j] = -2;
            }
        }
    }

    for(int i = 0; i < board.length; i++){
        for(int j = 0; j < board[i].length; j++){
            if(board[i][j] == -1)
                board[i][j] = 0;
            else if(board[i][j] == -2)
                board[i][j] = 1;
        }
    }
}

LeetCode - Find Peak Element

Question Definition

A peak element is an element that is greater than its neighbors.

LeetCode - Container With Most Water

Question Definition

Given n non-negative integers a1, a2, …, an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Find two lines, which together with x-axis forms a container, such that the container contains the most water.