# Leetcode 1020. Number of Enclaves

You are given two `m x n`

binary matrices `grid1`

and `grid2`

containing only `0`

's (representing water) and `1`

's (representing land). An **island** is a group of `1`

's connected **4-directionally** (horizontal or vertical). Any cells outside of the grid are considered water cells.

An island in `grid2`

is considered a **sub-island **if there is an island in `grid1`

that contains **all** the cells that make up **this** island in `grid2`

.

Return the *number** of islands in *`grid2`

*that are considered *** sub-islands**.

**Example 1:**

**Input:** grid1 = [[1,1,1,0,0],[0,1,1,1,1],[0,0,0,0,0],[1,0,0,0,0],[1,1,0,1,1]], grid2 = [[1,1,1,0,0],[0,0,1,1,1],[0,1,0,0,0],[1,0,1,1,0],[0,1,0,1,0]]

**Output:** 3

**Explanation: **In the picture above, the grid on the left is grid1 and the grid on the right is grid2.

The 1s colored red in grid2 are those considered to be part of a sub-island. There are three sub-islands.

**Example 2:**

**Input:** grid1 = [[1,0,1,0,1],[1,1,1,1,1],[0,0,0,0,0],[1,1,1,1,1],[1,0,1,0,1]], grid2 = [[0,0,0,0,0],[1,1,1,1,1],[0,1,0,1,0],[0,1,0,1,0],[1,0,0,0,1]]

**Output:** 2

**Explanation: **In the picture above, the grid on the left is grid1 and the grid on the right is grid2.

The 1s colored red in grid2 are those considered to be part of a sub-island. There are two sub-islands.

**Solution:**

class Solution {

public:

int rsize{0};

int csize{0};

int count{0};

vector<vector<int>> next{{1,0}, {-1,0}, {0,1}, {0,-1}};

int dfs(vector<vector<int>>& grid1, vector<vector<int>>& grid2, vector<vector<bool>>& visited, int r, int c, bool& sea) {

if (r == rsize || r < 0 || c == csize || c < 0 || visited[r][c] || grid2[r][c] == 0) {

return 0;

}

if (grid1[r][c] == 0) {

sea = true;

}visited[r][c] = true;

for (int i=0; i<4; i++) {

dfs(grid1, grid2, visited, r+next[i][0], c+next[i][1], sea);

}

if (sea)

return 0;

return 1;

}

int countSubIslands(vector<vector<int>>& grid1, vector<vector<int>>& grid2) {

rsize = grid1.size();

csize = grid1[0].size();

vector<vector<bool>> visited(rsize, vector<bool>(csize, false));

for (int i=0; i<rsize; i++) {

for (int j=0; j<csize; j++) {

if (grid1[i][j]) {

bool sea = false;

count += dfs(grid1, grid2, visited, i, j, sea);

}

}

}

return count;

}

};

Runtime: 393 ms, faster than 77.23% of C++ online submissions for Count Sub Islands.

Memory Usage: 90.3 MB, less than 63.61% of C++ online submissions for Count Sub Islands.