g0101_0200.s0200_number_of_islands.Solution.cpp Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

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// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Depth_First_Search
// #Breadth_First_Search #Matrix #Union_Find
// #Algorithm_II_Day_6_Breadth_First_Search_Depth_First_Search
// #Graph_Theory_I_Day_1_Matrix_Related_Problems #Level_1_Day_9_Graph/BFS/DFS #Udemy_Graph
// #Big_O_Time_O(M*N)_Space_O(M*N) #2024_05_26_Time_19_ms_(97.48%)_Space_15.7_MB_(92.21%)

#include 

class Solution {
public:
    int numIslands(std::vector>& grid) {
        int islands = 0;
        if (!grid.empty() && !grid[0].empty()) {
            for (int i = 0; i < grid.size(); i++) {
                for (int j = 0; j < grid[0].size(); j++) {
                    if (grid[i][j] == '1') {
                        dfs(grid, i, j);
                        islands++;
                    }
                }
            }
        }
        return islands;
    }

private:
    void dfs(std::vector>& grid, int x, int y) {
        if (x < 0 || x >= grid.size() || y < 0 || y >= grid[0].size() || grid[x][y] != '1') {
            return;
        }
        grid[x][y] = 'x';
        dfs(grid, x + 1, y);
        dfs(grid, x - 1, y);
        dfs(grid, x, y + 1);
        dfs(grid, x, y - 1);
    }
};