矩陣dfs--走回路
阿新 • • 發佈:2017-08-03
static [1] array || rpath args 元素 sys lis
矩陣dfs 走回路 的問題(最後沒有在回走---Corner case), 先想好算法, 再自己畫圖走一遍試試, 遞歸出口, 註意 corner case, 什麽時候符合題意, 什麽時候往裏面加元素, 邊走邊看需要 什麽工具,
工具: map(方向), 結果容器, visited, 輔助容器或變量
class Demo { List<String> curPath = new ArrayList<>(); int[][] dirs = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } }; private final Map<Integer, String> dirMap = new HashMap<>(); String[] dict = new String[]{"up", "right", "down", "left"}; private int count; public List<String> findPath(char[][] maze, int x, int y) { int m = maze.length; int n = maze[0].length; count = 0; for (int i = 0; i < m; i++) { for (int j = 0; j < n; j++) { if (maze[i][j] == ‘T‘) { count++; } } } boolean[][] visited = new boolean[m][n]; dfs(maze, x, y, visited); return count == 0 ? curPath : new ArrayList<>(); } private void dfs(char[][] maze, int x, int y, boolean[][] visited ) { if (maze[x][y] != ‘T‘ ) { return; } int m = maze.length; int n = maze[0].length; visited[x][y] = true; count--; for (int i = 0; i < 4; i++) { int xx = x + dirs[i][0]; int yy = y + dirs[i][1]; if (xx < 0 || xx >= m || yy < 0 || yy >= n || visited[xx][yy] || maze[xx][yy] == ‘F‘) { continue; } curPath.add(dict[i]); //curPath.add(dirMap.get(i)); // 為啥用map老是 空指針異常啊??? dfs(maze, xx, yy, visited); if (count != 0) { curPath.add(dict[(i + 2) % 4]); // 回路 } } } } public class Robot { public static void main(String[] args) { Demo r = new Demo(); char[][] maze = { {‘T‘, ‘T‘, ‘T‘, ‘F‘}, {‘F‘, ‘T‘, ‘F‘, ‘T‘}, {‘F‘, ‘T‘, ‘T‘, ‘F‘} }; List<String> res = r.findPath(maze, 1, 1); System.out.println(String.join(" ", res)); } }
矩陣dfs--走回路