featureLab/bitkylin-algorithm/section-4/leetcode4/NumberOfIslands.java at master · bitkylin/featureLab · GitHub

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/**
 * <p>给你一个由 <code>'1'</code>（陆地）和 <code>'0'</code>（水）组成的的二维网格，请你计算网格中岛屿的数量。</p>
 *
 * <p>岛屿总是被水包围，并且每座岛屿只能由水平方向和/或竖直方向上相邻的陆地连接形成。</p>
 *
 * <p>此外，你可以假设该网格的四条边均被水包围。</p>
 *
 * <p> </p>
 *
 * <p><strong>示例 1：</strong></p>
 *
 * <pre>
 * <strong>输入：</strong>grid = [
 * ["1","1","1","1","0"],
 * ["1","1","0","1","0"],
 * ["1","1","0","0","0"],
 * ["0","0","0","0","0"]
 * ]
 * <strong>输出：</strong>1
 * </pre>
 *
 * <p><strong>示例 2：</strong></p>
 *
 * <pre>
 * <strong>输入：</strong>grid = [
 * ["1","1","0","0","0"],
 * ["1","1","0","0","0"],
 * ["0","0","1","0","0"],
 * ["0","0","0","1","1"]
 * ]
 * <strong>输出：</strong>3
 * </pre>
 *
 * <p> </p>
 *
 * <p><strong>提示：</strong></p>
 *
 * <ul>
 * <li><code>m == grid.length</code></li>
 * <li><code>n == grid[i].length</code></li>
 * <li><code>1 <= m, n <= 300</code></li>
 * <li><code>grid[i][j]</code> 的值为 <code>'0'</code> 或 <code>'1'</code></li>
 * </ul>
 * <div><div>Related Topics</div><div><li>深度优先搜索</li><li>广度优先搜索</li><li>并查集</li><li>数组</li><li>矩阵</li></div></div><br><div><li>👍 1448</li><li>👎 0</li></div>
 */

package leetcode4;

public class NumberOfIslands {

    public static void main(String[] args) {
        Solution solution = new NumberOfIslands().new Solution();
    }

    /**
     * DFS，不会改变原数组
     */
    class Solution {
        public int numIslands(char[][] grid) {
            int res = 0;
            boolean[][] visit = new boolean[grid.length][grid[0].length];
            for (int i = 0; i < grid.length; i++) {
                for (int j = 0; j < grid[i].length; j++) {
                    if (grid[i][j] == '1' && !visit[i][j]) {
                        res++;
                        solve(grid, visit, i, j);
                    }
                }
            }
            return res;
        }

        private void solve(char[][] grid, boolean[][] visit, int i, int j) {
            if (i >= grid.length || i < 0 || j >= grid[i].length || j < 0 || grid[i][j] == '0' || visit[i][j]) {
                return;
            }
            visit[i][j] = true;
            solve(grid, visit, i + 1, j);
            solve(grid, visit, i - 1, j);
            solve(grid, visit, i, j + 1);
            solve(grid, visit, i, j - 1);
        }
    }

    /**
     * DFS，会改变原数组
     */
    class Solution1 {
        public int numIslands(char[][] grid) {
            int res = 0;
            for (int i = 0; i < grid.length; i++) {
                for (int j = 0; j < grid[i].length; j++) {
                    if (grid[i][j] == '1') {
                        res++;
                        solve(grid, i, j);
                    }
                }
            }
            return res;
        }

        private void solve(char[][] grid, int i, int j) {
            if (i >= grid.length || i < 0 || j >= grid[i].length || j < 0 || grid[i][j] == '0') {
                return;
            }
            grid[i][j] = '0';
            solve(grid, i + 1, j);
            solve(grid, i - 1, j);
            solve(grid, i, j + 1);
            solve(grid, i, j - 1);
        }
    }
}