feat: solved 289

Author: fghpdf

src/com/fghpdf/GameOfLife/Solution.java

@@ -0,0 +1,49 @@
+package com.fghpdf.GameOfLife;
+
+/**
+ * @author fghpdf
+ * @date 2019/12/25
+ * https://leetcode.com/problems/game-of-life/
+ * https://leetcode.com/problems/game-of-life/discuss/73223/Easiest-JAVA-solution-with-explanation
+ * 没懂
+ **/
+public class Solution {
+	public void gameOfLife(int[][] board) {
+		if (board == null || board.length == 0) {
+			return;
+		}
+		int m = board.length, n = board[0].length;
+
+		for (int i = 0; i < m; i++) {
+			for (int j = 0; j < n; j++) {
+				int lives = liveNeighbors(board, m, n, i, j);
+
+				// In the beginning, every 2nd bit is 0;
+				// So we only need to care about when will the 2nd bit become 1.
+				if (board[i][j] == 1 && lives >= 2 && lives <= 3) {
+					board[i][j] = 3; // Make the 2nd bit 1: 01 ---> 11
+				}
+				if (board[i][j] == 0 && lives == 3) {
+					board[i][j] = 2; // Make the 2nd bit 1: 00 ---> 10
+				}
+			}
+		}
+
+		for (int i = 0; i < m; i++) {
+			for (int j = 0; j < n; j++) {
+				board[i][j] >>= 1;  // Get the 2nd state.
+			}
+		}
+	}
+
+	public int liveNeighbors(int[][] board, int m, int n, int i, int j) {
+		int lives = 0;
+		for (int x = Math.max(i - 1, 0); x <= Math.min(i + 1, m - 1); x++) {
+			for (int y = Math.max(j - 1, 0); y <= Math.min(j + 1, n - 1); y++) {
+				lives += board[x][y] & 1;
+			}
+		}
+		lives -= board[i][j] & 1;
+		return lives;
+	}
+}