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package class_2022_12_2_week;
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// 来自亚马逊、谷歌、微软、Facebook、Bloomberg
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// 给你一个大小为 n x n 二进制矩阵 grid 。最多 只能将一格 0 变成 1 。
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// 返回执行此操作后，grid 中最大的岛屿面积是多少？
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// 岛屿 由一组上、下、左、右四个方向相连的 1 形成。
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// 测试链接 : https://leetcode.cn/problems/making-a-large-island/
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public class Code02_MakingALargeIsland {
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public static int largestIsland(int[][] grid) {
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int n = grid.length;
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int m = grid[0].length;
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int id = 2;
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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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if (grid[i][j] == 1) {
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infect(grid, i, j, id++, n, m);
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}
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}
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}
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// ? ? ?
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// 0 1 2 3 4 9
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int[] sizes = new int[id];
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int ans = 0;
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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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if (grid[i][j] > 1) {
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// grid[i][j] = 4
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// sizes[4]++
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ans = Math.max(ans, ++sizes[grid[i][j]]);
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}
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}
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}
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boolean[] visited = new boolean[id];
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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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if (grid[i][j] == 0) {
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int up = i - 1 >= 0 ? grid[i - 1][j] : 0;
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int down = i + 1 < n ? grid[i + 1][j] : 0;
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int left = j - 1 >= 0 ? grid[i][j - 1] : 0;
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int right = j + 1 < m ? grid[i][j + 1] : 0;
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int merge = 1 + sizes[up];
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visited[up] = true;
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if (!visited[down]) {
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merge += sizes[down];
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visited[down] = true;
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}
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if (!visited[left]) {
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merge += sizes[left];
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visited[left] = true;
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}
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if (!visited[right]) {
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merge += sizes[right];
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visited[right] = true;
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}
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ans = Math.max(ans, merge);
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visited[up] = false;
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visited[down] = false;
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visited[left] = false;
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visited[right] = false;
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}
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}
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}
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return ans;
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}
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// grid
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// (i,j) == 1 -> v
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// (i,j) != 1 -> return什么也不做！
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// (i,j) 越界，return什么也不做！
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public static void infect(int[][] grid, int i, int j, int v, int n, int m) {
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if (i < 0 || i == n || j < 0 || j == m || grid[i][j] != 1) {
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return;
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}
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// (i,j) 不越界，(i,j) == 1
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grid[i][j] = v;
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infect(grid, i - 1, j, v, n, m);
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infect(grid, i + 1, j, v, n, m);
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infect(grid, i, j - 1, v, n, m);
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infect(grid, i, j + 1, v, n, m);
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}
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}
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