2022-07-15 Daily-Challenge

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

July LeetCoding Challenge 15

Description

Max Area of Island

You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water.

The area of an island is the number of cells with a value 1 in the island.

Return the maximum area of an island in grid. If there is no island, return 0.

Example 1:

img

Input: grid = [[0,0,1,0,0,0,0,1,0,0,0,0,0],[0,0,0,0,0,0,0,1,1,1,0,0,0],[0,1,1,0,1,0,0,0,0,0,0,0,0],[0,1,0,0,1,1,0,0,1,0,1,0,0],[0,1,0,0,1,1,0,0,1,1,1,0,0],[0,0,0,0,0,0,0,0,0,0,1,0,0],[0,0,0,0,0,0,0,1,1,1,0,0,0],[0,0,0,0,0,0,0,1,1,0,0,0,0]]
Output: 6
Explanation: The answer is not 11, because the island must be connected 4-directionally.

Example 2:

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

Constraints:

  • m == grid.length
  • n == grid[i].length
  • 1 <= m, n <= 50
  • grid[i][j] is either 0 or 1.

Solution

const int moves[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
class Solution {
  int current;
  int rows;
  int cols;
  void dfs(vector<vector<int>>& grid, int row, int col) {
    grid[row][col] = 0;
    current += 1;
    for(int i = 0; i < 4; ++i) {
      int newRow = row + moves[i][0];
      int newCol = col + moves[i][1];
      if(newRow < 0 || newCol < 0 || newRow >= rows || newCol >= cols) continue;
      if(grid[newRow][newCol]) {
        dfs(grid, newRow, newCol);
      }
    }
  }
public:
  int maxAreaOfIsland(vector<vector<int>>& grid) {
    rows = grid.size();
    cols = grid.front().size();
    int answer = 0;
    for(int i = 0; i < rows; i++) {
      for(int j = 0; j < cols; j++) {
        if(grid[i][j]) {
          current = 0;
          dfs(grid, i, j);
          answer = max(answer, current);
        }
      }
    }
    return answer;
  }
};

// Accepted
// 728/728 cases passed (22 ms)
// Your runtime beats 82.07 % of cpp submissions
// Your memory usage beats 98.43 % of cpp submissions (23 MB)
Algorithm