1020. Number of Enclaves

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problem

solution

先將周圍島嶼淹沒，再去算剩下島嶼面積

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class Solution {
public:
    void dfs(vector<vector<int>> & grid, int i, int j){
        int n = grid.size(), m = grid[0].size();
        if(i<0 || i>n-1 || j<0 || j>m-1 || grid[i][j] == 0) return;
        grid[i][j] = 0;
        dfs(grid, i+1,j);
        dfs(grid, i-1,j);
        dfs(grid, i,j-1);
        dfs(grid, i,j+1);
    }
    int numEnclaves(vector<vector<int>>& grid) {
        int n = grid.size(), m = grid[0].size();
        for(int i=0;i<n;++i){
            dfs(grid, i, 0);
            dfs(grid, i, m-1);
        }
        for(int j=0;j<m ; ++j){
            dfs(grid, 0, j);
            dfs(grid, n-1,j);
        }
        
        int count =0 ;
        for(int i =1;i<n-1;++i){
            for(int j =1;j<m-1;++j){
                if(grid[i][j] == 1){
                    count++;
                }
            }
        }
        return count;
    }
};

analysis

  • time complexity O(n*m)
  • space complexity O(n*m)