Create 827. Making A Large Island (#702)

827. Making A Large Island

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+class Solution {
+public:
+    int largestIsland(vector<vector<int>>& grid) {
+        if (grid.empty())
+            return 0;
+
+        int n = grid.size();
+        vector<vector<int>> labels(n,vector<int>(n, 0));
+        unordered_map<int, int> islandSizes;
+        int label = 1;
+        int maxSize = 0;
+
+        int dirs[4][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
+
+        for (int i = 0; i < n; ++i) {
+            for (int j = 0; j < n; ++j) {
+                if (grid[i][j] == 1 && labels[i][j] == 0) {
+                    int size = 0;
+                    vector<pair<int, int>> stack;
+                    stack.push_back({i, j});
+                    labels[i][j] = label;
+
+                    while (!stack.empty()) {
+                        auto [x, y] = stack.back();
+                        stack.pop_back();
+                        size++;
+
+                        for (auto [dx, dy] : dirs) {
+                            int nx = x + dx, ny = y + dy;
+                            if (nx >= 0 && nx < n && ny >= 0 && ny < n &&
+                                grid[nx][ny] == 1 && labels[nx][ny] == 0) {
+                                labels[nx][ny] = label;
+                                stack.push_back({nx, ny});
+                            }
+                        }
+                    }
+
+                    islandSizes[label] = size;
+                    maxSize = max(maxSize, size);
+                    label++;
+                }
+            }
+        }
+
+        for (int i = 0; i < n; ++i) {
+            for (int j = 0; j < n; ++j) {
+                if (grid[i][j] == 0) {
+                    unordered_set<int> neighborLabels;
+                    int total = 1;
+
+                    for (auto [dx, dy] : dirs) {
+                        int nx = i + dx, ny = j + dy;
+                        if (nx >= 0 && nx < n && ny >= 0 && ny < n &&
+                            grid[nx][ny] == 1) {
+                            neighborLabels.insert(labels[nx][ny]);
+                        }
+                    }
+
+                    for (int lbl : neighborLabels) {
+                        total += islandSizes[lbl];
+                    }
+
+                    maxSize = max(maxSize, total);
+                }
+            }
+        }
+
+        return maxSize;
+    }
+};