LeetCode Game of Life

LeetCode Game of Life

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.

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?

1. 活着的细胞周围有少于2个活着的细胞，则该细胞死亡
2. 活着的细胞周围有2个或3个活着的细胞，则该细胞继续活着
3. 活着的细胞周围有多于3个活着的细胞，则该细胞死亡
4. 死亡的细胞周围有3个活着的细胞，则该细胞复活

• 0：0→0，原来死亡，现在还死亡
• 1：1→1，原来活着，现在还活着
• 2：1→0，原来活着，现在死亡
• 3：0→1，原来死亡，现在活着

class Solution {
public:
void gameOfLife(vector<vector<int>>& board) {
int m = board.size(), n = 0;
if (m != 0)n = board[0].size();
if (m == 0 || n == 0)return;
vector<vector<int>> dirs = { {-1,-1},{-1,0},{-1,1},{0,-1},{0,1},{1,-1},{1,0},{1,1} };
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
int lives = 0;
for (int k = 0; k < dirs.size(); ++k) {
int x = i + dirs[k][0], y = j + dirs[k][1];
if (x >= 0 && x < m&&y >= 0 && y < n && (board[x][y] == 1 || board[x][y] == 2))++lives;
}
if (board[i][j] == 1 || board[i][j] == 2) {
if (lives < 2 || lives > 3)board[i][j] = 2;
else board[i][j] = 1;
}
else if (lives == 3)board[i][j] = 3;
}
}
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
board[i][j] %= 2;
}
}
}
};