左程云大厂算法刷题班—

第一题

leetcode499：迷宫2
思路：宽度优先遍历

public class 第一题15 {public static void main(String[] args) {int[][] maze = {{0,0,0,0,0},{1,1,0,0,1},{0,0,0,0,0},{0,1,0,0,1},{0,1,0,0,0}};int[] hole = {0,1};int[] ball = {4,3};String res = findShortestWay(maze, hole, ball);System.out.println(res);}public static int[][] to = {{1,0},{0,-1},{0,1},{-1,0},{0,0}};public static String[] re = {"d","l","r","u"};static class Node{public int x;public int y;public int d;//0,1,2,3,4   4 代表初始位置public String p;//路径public Node(int x,int y,int d,String p){this.x = x;this.y = y;this.d = d;this.p = p;}}public static String findShortestWay(int[][] maze,int[] hole,int[] ball){int n = maze.length;int m = maze[0].length;boolean[][][] visit = new boolean[n][m][4];int s1 = 0;int s2 = 0;Node[] p1 = new Node[n * m];Node[] p2 = new Node[n * m];s1 = spread(maze,n,m,visit,new Node(ball[0],ball[1],4,""),p1,s1);while (s1 != 0){for (int i = 0;i < s1;i++){Node cur = p1[i];if (cur.x == hole[0] && cur.y == hole[1]){return cur.p;}s2 = spread(maze,n,m,visit,cur,p2,s2);}Node[] temp = p1;p1 = p2;p2 = temp;s1 = s2;s2 = 0;}return "impossible";}private static int spread(int[][] maze, int n, int m, boolean[][][] visit, Node cur, Node[] p2, int s2) {int d = cur.d;int x = cur.x + to[d][0];int y = cur.y + to[d][1];if (d == 4 || x < 0 || x == n || y < 0 || y == m || maze[x][y] != 0){for (int i = 0;i < 4;i++){if (i != d){x = cur.x + to[i][0];y = cur.y + to[i][1];if (x >= 0 && x < n && y >= 0 && y < m && !visit[x][y][i]){visit[x][y][i] = true;p2[s2++] = new Node(x,y,i,cur.p + re[i]);}}}}else {if (!visit[x][y][d]){visit[x][y][d] = true;p2[s2++] = new Node(x,y,d,cur.p);}}return s2;}
}

第二题

leetcode446. 等差数列划分 II - 子序列

public class 第二题15 {public static int numberOfArithmeticSlices(int[] nums) {int n = nums.length;if (n < 3){return 0;}HashMap<Long,Integer>[] dp = new HashMap[n];for (int i = 0;i < n;i++){dp[i] = new HashMap<>();}int res = 0;for (int i = 1;i < n;i++){for (int j = 0;j < i;j++){long diff = (long) nums[i] - nums[j];if (diff > Integer.MAX_VALUE || diff < Integer.MIN_VALUE){continue;}dp[i].put(diff,dp[i].getOrDefault(diff,0) + dp[j].getOrDefault(diff,0) + 1);if (dp[j].containsKey(diff)){res += dp[j].get(diff);}}}return res;}
}

第三题

leetcode489. 扫地机器人

public class 第三题15 {interface Robot{public boolean move();public void turnLeft();public void turnRight();public void clean();}public static int[][] ds = {{-1,0},{0,1},{1,0},{0,-1}};public static void cleanRoom(Robot robot){clean(robot,0,0,0,new HashSet<String>());}private static void clean(Robot robot, int x, int y, int d, HashSet<String> visited) {robot.clean();visited.add(x + "_" + y);for (int i = 0;i < 4;i++){int nd = (d + i) % 4;int nx = x + ds[i][0];int ny = y + ds[i][1];if (robot.move() && !visited.contains(nx + "_" + ny)){clean(robot,nx,ny,nd,visited);}robot.turnRight();}robot.turnRight();robot.turnRight();robot.move();robot.turnRight();robot.turnRight();}
}

第四题

leetcode875. 爱吃香蕉的珂珂
思路：二分

public class 第四题15 {public static void main(String[] args) {int i = 805306368 * 3;System.out.println(i);}public int minEatingSpeed(int[] piles, int h) {int maxValue = 1;for (int pile : piles){maxValue = Math.max(pile,maxValue);}int l = 1;int r = maxValue;int lastTime = maxValue;while (l <= r){int mid = (l + r) / 2;if (calculateSum(piles,mid) > h){l = mid + 1;}else {lastTime = mid;r = mid - 1;}}return lastTime;}private int calculateSum(int[] piles, int mid) {int res = 0;for (int i = 0;i < piles.length;i++){res += (piles[i] + mid - 1) / mid;}return res;}
}

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左程云大厂算法刷题班——15

第一题

第二题

第三题

第四题

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