modify code

算法周更班/class_2021_12_3_week/Code04_CutOffTreesForGolfEvent.java

@@ -1,74 +1,141 @@
 package class_2021_12_3_week;
 
-import java.util.ArrayList;
-import java.util.LinkedList;
+import java.util.Arrays;
 import java.util.List;
 
+// leetcode增加了新的数据
+// 导致原来的实现不通过了
+// 一怒之下，做了各种优化
+// 思路完全和课上讲的一样，就是实现完全重来了
+// 目前打败100%的人
 // 测试链接 : https://leetcode.com/problems/cut-off-trees-for-golf-event/
 public class Code04_CutOffTreesForGolfEvent {
 
+	public static int MAXN = 51;
+	public static int MAXM = 51;
+	public static int LIMIT = MAXN * MAXM;
+	public static int[][] f = new int[MAXN][MAXM];
+	public static int[][] arr = new int[LIMIT][3];
+	public static int[] move = new int[] { 1, 0, -1, 0, 1 };
+	public static int n, m;
+
+	// 为了快，手撸双端队列
+	public static int[][] deque = new int[LIMIT][3];
+	// 双端队列的头、尾、大小
+	public static int l, r, size;
+
+	// 初始化双端队列
+	public static void buildDeque() {
+		l = -1;
+		r = -1;
+		size = 0;
+	}
+
+	// 双端队列从头部弹出
+	public static int[] pollFirst() {
+		int[] ans = deque[l];
+		if (l < LIMIT - 1) {
+			l++;
+		} else {
+			l = 0;
+		}
+		size--;
+		if (size == 0) {
+			l = r = -1;
+		}
+		return ans;
+	}
+
+	// 双端队列从头部加入
+	public static void offerFirst(int x, int y, int d) {
+		if (l == -1) {
+			deque[0][0] = x;
+			deque[0][1] = y;
+			deque[0][2] = d;
+			l = r = 0;
+		} else {
+			int fill = l == 0 ? (LIMIT - 1) : (l - 1);
+			deque[fill][0] = x;
+			deque[fill][1] = y;
+			deque[fill][2] = d;
+			l = fill;
+		}
+		size++;
+	}
+
+	// 双端队列从尾部加入
+	public static void offerLast(int x, int y, int d) {
+		if (l == -1) {
+			deque[0][0] = x;
+			deque[0][1] = y;
+			deque[0][2] = d;
+			l = r = 0;
+		} else {
+			int fill = (r == LIMIT - 1) ? 0 : (r + 1);
+			deque[fill][0] = x;
+			deque[fill][1] = y;
+			deque[fill][2] = d;
+			r = fill;
+		}
+		size++;
+	}
+
 	public static int cutOffTree(List<List<Integer>> forest) {
-		int n = forest.size();
-		int m = forest.get(0).size();
-		// [ [3,5,2], [1,9,4] , [2,6,10] ]
-		// 低 中 高
-		ArrayList<int[]> cells = new ArrayList<>();
+		n = forest.size();
+		m = forest.get(0).size();
+		int cnt = 0;
 		for (int i = 0; i < n; i++) {
 			for (int j = 0; j < m; j++) {
-				int val = forest.get(i).get(j);
-				if (val > 1) {
-					cells.add(new int[] { i, j, val });
+				int value = forest.get(i).get(j);
+				f[i][j] = value > 0 ? 1 : 0;
+				if (value > 1) {
+					arr[cnt][0] = value;
+					arr[cnt][1] = i;
+					arr[cnt++][2] = j;
 				}
 			}
 		}
-		cells.sort((a, b) -> a[2] - b[2]);
-		int ans = 0, lastR = 0, lastC = 0;
-		for (int[] cell : cells) {
-			int step = bestWalk(forest, lastR, lastC, cell[0], cell[1]);
+		Arrays.sort(arr, 0, cnt, (a, b) -> a[0] - b[0]);
+		int ans = 0;
+		for (int i = 0, x = 0, y = 0, block = 2; i < cnt; i++, block++) {
+			int toX = arr[i][1];
+			int toY = arr[i][2];
+			int step = walk(x, y, toX, toY, block);
 			if (step == -1) {
 				return -1;
 			}
 			ans += step;
-			lastR = cell[0];
-			lastC = cell[1];
-			forest.get(lastR).set(lastC, 1);
+			x = toX;
+			y = toY;
 		}
 		return ans;
 	}
 
-	public static int[] next = { -1, 0, 1, 0, -1 };
-
-	// 0 1 2 3 4
-	// i
-	// 行 + next[i-1]
-	// 列 + next[i]
-	// i == 1 -> 上
-	// i == 2 -> 右
-	// i == 3 -> 下
-	// i == 4 -> 左
-	public static int bestWalk(List<List<Integer>> forest, int sr, int sc, int tr, int tc) {
-		int n = forest.size();
-		int m = forest.get(0).size();
-		boolean[][] seen = new boolean[n][m];
-		LinkedList<int[]> deque = new LinkedList<>();
-		deque.offerFirst(new int[] { 0, sr, sc });
-		while (!deque.isEmpty()) {
-			int[] cur = deque.pollFirst();
-			int step = cur[0], r = cur[1], c = cur[2];
-			if (r == tr && c == tc) {
-				return step;
-			}
-			seen[r][c] = true;
-			for (int i = 1; i < 5; i++) { // (r,c) 上下左右，全试试！
-				int nr = r + next[i - 1];
-				int nc = c + next[i];
-				if (nr >= 0 && nr < n && nc >= 0 && nc < m && !seen[nr][nc] && forest.get(nr).get(nc) > 0) {
-					int[] move = { step + 1, nr, nc };
-					// 更近的话
-					if ((i == 1 && r > tr) || (i == 2 && c < tc) || (i == 3 && r < tr) || (i == 4 && c > tc)) {
-						deque.offerFirst(move);
-					} else { // 更远的话，放到尾部！
-						deque.offerLast(move);
+	public static int walk(int a, int b, int c, int d, int block) {
+		buildDeque();
+		offerFirst(a, b, 0);
+		while (size > 0) {
+			int[] cur = pollFirst();
+			int x = cur[0];
+			int y = cur[1];
+			int distance = cur[2];
+			if (f[x][y] != block) {
+				f[x][y] = block;
+				if (x == c && y == d) {
+					return distance;
+				}
+				for (int i = 1; i < 5; i++) {
+					int nextX = x + move[i];
+					int nextY = y + move[i - 1];
+					if (nextX >= 0 && nextX < n && nextY >= 0 && nextY < m && f[nextX][nextY] != 0
+							&& f[nextX][nextY] != block) {
+						if ((i == 1 && y < d) || (i == 2 && x > c) || (i == 3 && y > d) || (i == 4 && x < c)) {
+							// 离的更近
+							offerFirst(nextX, nextY, distance + 1);
+						} else {
+							// 离的更远
+							offerLast(nextX, nextY, distance + 1);
+						}
 					}
 				}
 			}