leetcode827. 最大人工岛

骑猪看日落 2024-03-26 10:43 44阅读 0赞

> [牛客华为机试题库【题号 HJ开头】（重点看）][HJ]  
> [牛客在线编程算法篇【题号NC开头】][NC]  
> [剑指offer【题号 JZ开头】][offer_ JZ]  
> [力扣][Link 1]

### 1）[原题链接][Link 2] ###

### 2）已有题解 ###

### 3）代码 ###

package dfs;
    
    import java.util.HashMap;
    import java.util.HashSet;
    import java.util.Map;
    import java.util.Set;
    
    /**
     * 827. 最大人工岛
     */
    public class Leetcode827MakingALargeIsland {
        
        public static void main(String[] args) {
        
            int[][] grid = {
        {
        0, 0, 1}, {
        0, 1, 1}, {
        1, 0, 1}};
            Leetcode827MakingALargeIsland leetcode695MaxAreaOfIsland = new Leetcode827MakingALargeIsland();
            leetcode695MaxAreaOfIsland.largestIsland(grid);
        }
    
        public int largestIsland(int[][] grid) {
        
            // 收集所有岛屿的面积
            int islandNum = 2; //每个岛的标号设置成不一致，编号初始值为2
            Map<Integer, Integer> map = new HashMap<>();
            for (int i = 0; i < grid.length; i++) {
        
                for (int j = 0; j < grid[i].length; j++) {
        
                    if (grid[i][j] == 1) {
        
                        int area = dfs(grid, i, j, islandNum); //求当前岛屿的面积
                        if (area > 0) {
        
                            map.put(islandNum, area); //岛屿编号-->岛屿面积
                        }
                        islandNum++; // 存储完当前岛屿，改变岛屿编号存储下一个
                    }
                }
            }
    
            // 对所有位置进行填充,获取最大的联通面积
            int maxArea = 0;
            for (int i = 0; i < grid.length; i++) {
        
                for (int j = 0; j < grid[i].length; j++) {
        
                    maxArea = Math.max(maxArea, plusArea(grid, i, j, map));
                }
            }
            return maxArea;
        }
    
        int dfs(int[][] grid, int row, int column, int islandNum) {
        
            if (!isInGrid(grid, row, column)) {
        
                return 0;// 不在网格内
            }
            if (grid[row][column] == 0) {
        
                return 0; // '0'（水）
            }
            if (grid[row][column] != 1) {
        
                return 0; // 如果已经取过了则返回
            }
            grid[row][column] = islandNum; //给岛屿的这块土地编号，表示已经走过
    
            // 当前节点面积+上、下、左、右四个相邻结点引申出去计算得到的面积
            return 1 + dfs(grid, row - 1, column, islandNum)
                    + dfs(grid, row + 1, column, islandNum)
                    + dfs(grid, row, column - 1, islandNum)
                    + dfs(grid, row, column + 1, islandNum);
        }
    
        boolean isInGrid(int[][] grid, int row, int column) {
        
            return 0 <= row && row < grid.length && 0 <= column && column < grid[row].length;
        }
    
    
        public int plusArea(int[][] grid, int row, int column, Map<Integer, Integer> map) {
        
            if (grid[row][column] != 0) {
         //如果不是海洋 就不去填海，直接返回当前岛屿的面积
                return map.get(grid[row][column]);
            }
    
            // 当前节点填海以后会连同上、下、左、右四个相邻结点所在的岛屿联通，找出可以连接的岛屿
            Set<Integer> set = new HashSet<>();// 把当前海洋上所有的所有陆地编号找到，至于为啥用set,是避免把同一个岛屿取两回
            if (isInGrid(grid, row - 1, column) && grid[row - 1][column] != 0) {
        
                set.add(grid[row - 1][column]);
            }
            if (isInGrid(grid, row + 1, column) && grid[row + 1][column] != 0) {
        
                set.add(grid[row + 1][column]);
            }
            if (isInGrid(grid, row, column - 1) && grid[row][column - 1] != 0) {
        
                set.add(grid[row][column - 1]);
            }
            if (isInGrid(grid, row, column + 1) && grid[row][column + 1] != 0) {
        
                set.add(grid[row][column + 1]);
            }
    
            // 把联通的岛屿的面积加和
            int res = 0;
            for (Integer integer : set) {
        
                res += map.get(integer);
            }
    
            return res + 1; // 四周面积+当前节点面积→连在一起的最大面积
        }
    }

[HJ]: https://www.nowcoder.com/exam/oj/ta?tpId=37
[NC]: https://www.nowcoder.com/exam/oj
[offer_ JZ]: https://www.nowcoder.com/exam/oj/ta?page=1&tpId=13&type=13
[Link 1]: https://leetcode.cn/problemset/all/
[Link 2]: https://leetcode.cn/problems/making-a-large-island/