LeetCode #827: Making A Large Island

Author: ISKU

LeetCode/827/Solution.java

@@ -0,0 +1,102 @@
+/*
+ * Author: Minho Kim (ISKU)
+ * Date: November 14, 2019
+ * E-mail: minho.kim093@gmail.com
+ *
+ * https://github.com/ISKU/Algorithm
+ * https://leetcode.com/problems/making-a-large-island/
+ */
+
+class Solution {
+
+private final int[] dy = { 1, -1, 0, 0 };
+private final int[] dx = { 0, 0, 1, -1 };
+
+private int[][] map;
+private boolean[][] visited;
+
+private Map<Point, Integer> groupMap;
+private int[] count;
+private int Y, X, answer;
+
+public int largestIsland(int[][] grid) {
+map = grid;
+Y = map.length;
+X = map[0].length;
+groupMap = new HashMap<>();
+
+int groupNumber = 0;
+count = new int[2500];
+visited = new boolean[Y][X];
+for (int y = 0; y < Y; y++)
+for (int x = 0; x < X; x++)
+if (!visited[y][x] && map[y][x] == 1)
+dfs(y, x, groupNumber++);
+
+for (int y = 0; y < Y; y++) {
+for (int x = 0; x < X; x++) {
+if (map[y][x] == 1)
+continue;
+
+Set<Integer> set = new HashSet<>();
+for (int i = 0; i < 4; i++) {
+int ny = y + dy[i];
+int nx = x + dx[i];
+if (ny < 0 || ny >= Y || nx < 0 || nx >= X || map[ny][nx] == 0)
+continue;
+
+Point p = new Point(ny, nx);
+int group = groupMap.get(p);
+set.add(group);
+}
+
+int sum = 0;
+if (!set.isEmpty())
+for (int group : set)
+sum += count[group];
+
+answer = Math.max(answer, sum + 1);
+}
+}
+
+return answer;
+}
+
+private void dfs(int y, int x, int group) {
+visited[y][x] = true;
+groupMap.put(new Point(y, x), group);
+count[group]++;
+answer = Math.max(answer, count[group]);
+
+for (int i = 0; i < 4; i++) {
+int ny = y + dy[i];
+int nx = x + dx[i];
+if (ny < 0 || ny >= Y || nx < 0 || nx >= X || visited[ny][nx] || map[ny][nx] == 0)
+continue;
+
+dfs(ny, nx, group);
+}
+}
+
+private class Point {
+public int y, x;
+
+public Point(int y, int x) {
+this.y = y;
+this.x = x;
+}
+
+@Override
+public int hashCode() {
+return y * 2500 + x;
+}
+
+@Override
+public boolean equals(Object o) {
+Point p = (Point) o;
+if (this.y == p.y && this.x == p.x)
+return true;
+return false;
+}
+}
+}