Today I have done leetcode's April LeetCoding Challenge with cpp.

April LeetCoding Challenge 19

Description

Number of Islands

Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.

An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

Input: grid = [
  ["1","1","1","1","0"],
  ["1","1","0","1","0"],
  ["1","1","0","0","0"],
  ["0","0","0","0","0"]
]
Output: 1

Example 2:

Input: grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
Output: 3

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 300
• grid[i][j] is '0' or '1'.

Solution

class Solution {
  int move[4][2] = {{1,0},{0,1},{-1,0},{0,-1}};
  int height;
  int width;
  vector<vector<bool>> visited;
  void dfs(vector<vector<char>>& grid, int h, int w) {
    grid[h][w] = '0';
    for(int i = 0; i < 4; ++i) {
      int newH = h + move[i][0];
      int newW = w + move[i][1];
      if(newH >= 0 && newH < height && newW >= 0 && newW < width &&
         grid[newH][newW] == '1') {
        dfs(grid, newH, newW);
      }
    }
  }
public:
  int numIslands(vector<vector<char>>& grid) {
    height = grid.size();
    width = grid[0].size();
    int ans = 0;
    for(int i = 0; i < height; ++i) {
      for(int j = 0; j < width; ++j) {
        if(grid[i][j] == '1') {
          ans += 1;
          dfs(grid, i, j);
        }
      }
    }
    return ans;
  }
};

// Accepted
// 49/49 cases passed (66 ms)
// Your runtime beats 35.13 % of cpp submissions
// Your memory usage beats 97.03 % of cpp submissions (12.2 MB)