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80 lines
2.1 KiB
80 lines
2.1 KiB
package class_2021_12_3_week;
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import java.util.ArrayList;
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import java.util.LinkedList;
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import java.util.List;
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// 测试链接 : https://leetcode.com/problems/cut-off-trees-for-golf-event/
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public class Code04_CutOffTreesForGolfEvent {
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public static int cutOffTree(List<List<Integer>> forest) {
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int n = forest.size();
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int m = forest.get(0).size();
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// [ [3,5,2], [1,9,4] , [2,6,10] ]
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// 低 中 高
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ArrayList<int[]> cells = new ArrayList<>();
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for (int i = 0; i < n; i++) {
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for (int j = 0; j < m; j++) {
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int val = forest.get(i).get(j);
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if (val > 1) {
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cells.add(new int[] { i, j, val });
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}
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}
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}
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cells.sort((a, b) -> a[2] - b[2]);
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int ans = 0, lastR = 0, lastC = 0;
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for (int[] cell : cells) {
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int step = bestWalk(forest, lastR, lastC, cell[0], cell[1]);
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if (step == -1) {
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return -1;
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}
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ans += step;
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lastR = cell[0];
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lastC = cell[1];
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forest.get(lastR).set(lastC, 1);
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}
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return ans;
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}
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public static int[] next = { -1, 0, 1, 0, -1 };
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// 0 1 2 3 4
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// i
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// 行 + next[i-1]
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// 列 + next[i]
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// i == 1 -> 上
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// i == 2 -> 右
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// i == 3 -> 下
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// i == 4 -> 左
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public static int bestWalk(List<List<Integer>> forest, int sr, int sc, int tr, int tc) {
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int n = forest.size();
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int m = forest.get(0).size();
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boolean[][] seen = new boolean[n][m];
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LinkedList<int[]> deque = new LinkedList<>();
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deque.offerFirst(new int[] { 0, sr, sc });
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while (!deque.isEmpty()) {
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int[] cur = deque.pollFirst();
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int step = cur[0], r = cur[1], c = cur[2];
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if (r == tr && c == tc) {
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return step;
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}
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seen[r][c] = true;
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for (int i = 1; i < 5; i++) { // (r,c) 上下左右，全试试！
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int nr = r + next[i - 1];
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int nc = c + next[i];
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if (nr >= 0 && nr < n && nc >= 0 && nc < m && !seen[nr][nc] && forest.get(nr).get(nc) > 0) {
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int[] move = { step + 1, nr, nc };
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// 更近的话
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if ((i == 1 && r > tr) || (i == 2 && c < tc) || (i == 3 && r < tr) || (i == 4 && c > tc)) {
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deque.offerFirst(move);
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} else { // 更远的话，放到尾部！
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deque.offerLast(move);
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}
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}
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}
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}
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return -1;
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}
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}
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