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leetcode_java/src/main/java/LeetCodeJava/BFS/MinimumKnightMoves.java
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| package LeetCodeJava.BFS; | ||
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| // https://leetcode.com/problems/minimum-knight-moves/description/ | ||
| // https://leetcode.ca/all/1197.html | ||
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| import java.util.ArrayDeque; | ||
| import java.util.HashSet; | ||
| import java.util.LinkedList; | ||
| import java.util.Queue; | ||
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| /** | ||
| * 1197. Minimum Knight Moves | ||
| * In an infinite chess board with coordinates from -infinity to +infinity, you have a knight at square [0, 0]. | ||
| * <p> | ||
| * A knight has 8 possible moves it can make, as illustrated below. Each move is two squares in a cardinal direction, then one square in an orthogonal direction. | ||
| * <p> | ||
| * <p> | ||
| * <p> | ||
| * Return the minimum number of steps needed to move the knight to the square [x, y]. It is guaranteed the answer exists. | ||
| * <p> | ||
| * <p> | ||
| * <p> | ||
| * Example 1: | ||
| * <p> | ||
| * Input: x = 2, y = 1 | ||
| * Output: 1 | ||
| * Explanation: [0, 0] → [2, 1] | ||
| * Example 2: | ||
| * <p> | ||
| * Input: x = 5, y = 5 | ||
| * Output: 4 | ||
| * Explanation: [0, 0] → [2, 1] → [4, 2] → [3, 4] → [5, 5] | ||
| * <p> | ||
| * <p> | ||
| * Constraints: | ||
| * <p> | ||
| * |x| + |y| <= 300 | ||
| * Difficulty: | ||
| * Medium | ||
| * Lock: | ||
| * Prime | ||
| * Company: | ||
| * Amazon Facebook Google Oracle | ||
| * Problem Solution | ||
| * 1197-Minimum-Knight-Moves | ||
| */ | ||
| public class MinimumKnightMoves { | ||
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| // V0 | ||
| // IDEA : BFS | ||
| // TODO : fix and validate | ||
| // public int minKnightMoves(int x, int y) { | ||
| // | ||
| // if (x==0 && y==0){ | ||
| // return 0; | ||
| // } | ||
| // | ||
| // // init | ||
| // int[][] moves = new int[][]{ {1,2}, {2,1}, {2,-1}, {1,-2}, {-1,-2}, {-2,-1}, {-2,1}, {-1,2} }; | ||
| // // queue : FIFO | ||
| // Queue<List<Integer>> q = new LinkedList<>(); // Queue([x, y, step]) | ||
| // List<Integer> tmp = new ArrayList<>(); | ||
| // tmp.add(0); // x | ||
| // tmp.add(0); // y | ||
| // tmp.add(0); // step | ||
| // q.add(tmp); | ||
| // | ||
| // while(!q.isEmpty()){ | ||
| // List<Integer> cur = q.poll(); | ||
| // int cur_x = cur.get(0); | ||
| // int cur_y = cur.get(1); | ||
| // int cur_step = cur.get(2); | ||
| // if (cur_x == x && cur_y == y){ | ||
| // return cur_step; | ||
| // } | ||
| // for (int[] move : moves){ | ||
| // List<Integer> newCoor = new ArrayList<>(); | ||
| // newCoor.add(cur_x + move[0]); | ||
| // newCoor.add(cur_y + move[1]); | ||
| // newCoor.add(cur_step + 1); | ||
| // q.add(newCoor); | ||
| // } | ||
| // } | ||
| // | ||
| // return -1; | ||
| // } | ||
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| // V1 | ||
| // IDEA : BFS | ||
| // https://leetcode.ca/2019-03-11-1197-Minimum-Knight-Moves/ | ||
| public int minKnightMoves_1(int x, int y) { | ||
| x += 310; | ||
| y += 310; | ||
| int ans = 0; | ||
| Queue<int[]> q = new ArrayDeque<>(); | ||
| q.offer(new int[]{310, 310}); | ||
| // NOTE !!! use vis (boolean 2D array) to AVOID visit same coordination again | ||
| boolean[][] vis = new boolean[700][700]; | ||
| vis[310][310] = true; | ||
| int[][] dirs = {{-2, 1}, {-1, 2}, {1, 2}, {2, 1}, {2, -1}, {1, -2}, {-1, -2}, {-2, -1}}; | ||
| while (!q.isEmpty()) { | ||
| for (int k = q.size(); k > 0; --k) { | ||
| int[] p = q.poll(); | ||
| if (p[0] == x && p[1] == y) { | ||
| return ans; | ||
| } | ||
| for (int[] dir : dirs) { | ||
| int c = p[0] + dir[0]; | ||
| int d = p[1] + dir[1]; | ||
| if (!vis[c][d]) { | ||
| vis[c][d] = true; | ||
| q.offer(new int[]{c, d}); | ||
| } | ||
| } | ||
| } | ||
| ++ans; | ||
| } | ||
| return -1; | ||
| } | ||
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| // V2 | ||
| // IDEA : BFD | ||
| // https://www.cnblogs.com/cnoodle/p/12820573.html | ||
| public int minKnightMoves_2(int x, int y) { | ||
| int[][] dirs = new int[][]{{-1, -2}, {-1, 2}, {1, -2}, {1, 2}, {-2, -1}, {-2, 1}, {2, -1}, {2, 1}}; | ||
| x = Math.abs(x); | ||
| y = Math.abs(y); | ||
| HashSet<String> visited = new HashSet<>(); | ||
| Queue<int[]> queue = new LinkedList<>(); | ||
| queue.offer(new int[]{0, 0}); | ||
| visited.add("0,0"); | ||
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| int step = 0; | ||
| while (!queue.isEmpty()) { | ||
| int size = queue.size(); | ||
| while (size-- > 0) { | ||
| int[] cur = queue.poll(); | ||
| if (cur[0] == x && cur[1] == y) { | ||
| return step; | ||
| } | ||
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| for (int[] dir : dirs) { | ||
| int i = cur[0] + dir[0]; | ||
| int j = cur[1] + dir[1]; | ||
| // (0, 0) -> (2, -1) -> (1, 1) | ||
| // +2的意思是多给两个格子的空间以便于骑士跳出去再跳回来的操作 | ||
| if (!visited.contains(i + "," + j) && i >= -1 && j >= -1 && i <= x + 2 && j <= y + 2) { | ||
| queue.offer(new int[]{i, j}); | ||
| visited.add(i + "," + j); | ||
| } | ||
| } | ||
| } | ||
| step++; | ||
| } | ||
| return -1; | ||
| } | ||
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| } |
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