695. Max Area of Island

695-max-area-of-island/memo.md

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+### step1
+
+200. Number of Islandsを参考に、1のマスに当たるたびに隣接するマスを辿ってareaの大きさを計算する方針で実装。
+
+### step2
+
+fという関数の名前をcountAreaに変更。
+
+### step3
+
+3回通すまで書き直し。

695-max-area-of-island/step1.cpp

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+class Solution {
+public:
+    int m, n;
+
+    void f(vector<vector<int>>& grid, int x, int y, int& val) {
+        if (x < 0 || x >= m || y < 0 || y >= n || grid[x][y] == 0) {
+            return;
+        }
+        grid[x][y] = 0;
+        val++;
+        f(grid, x + 1, y, val);
+        f(grid, x - 1, y, val);
+        f(grid, x, y + 1, val);
+        f(grid, x, y - 1, val);
+    }
+
+    int maxAreaOfIsland(vector<vector<int>>& grid) {
+        m = grid.size();
+        n = grid[0].size();
+        int maxArea = 0;
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                if (grid[i][j] == 1) {
+                    int val = 0;
+                    f(grid, i, j, val);
+                    maxArea = max(maxArea, val);
+                }
+            }
+        }
+        return maxArea;
+    }
+};

695-max-area-of-island/step2.cpp

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+class Solution {
+public:
+    int m, n;
+
+    void countArea(vector<vector<int>>& grid, int x, int y, int& val) {
+        if (x < 0 || x >= m || y < 0 || y >= n || grid[x][y] == 0) {
+            return;
+        }
+        grid[x][y] = 0;
+        val++;
+        countArea(grid, x + 1, y, val);
+        countArea(grid, x - 1, y, val);
+        countArea(grid, x, y + 1, val);
+        countArea(grid, x, y - 1, val);
+    }
+
+    int maxAreaOfIsland(vector<vector<int>>& grid) {
+        m = grid.size();
+        n = grid[0].size();
+        int maxArea = 0;
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                if (grid[i][j] == 1) {
+                    int val = 0;
+                    countArea(grid, i, j, val);
+                    maxArea = max(maxArea, val);
+                }
+            }
+        }
+        return maxArea;
+    }
+};

695-max-area-of-island/step3.cpp

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+class Solution {
+public:
+    int m, n;
+
+    void countArea(vector<vector<int>>& grid, int x, int y, int& val) {
+        if (x < 0 || x >= m || y < 0 || y >= n || grid[x][y] == 0) {
+            return;
+        }
+        grid[x][y] = 0;
+        val++;
+        countArea(grid, x + 1, y, val);
+        countArea(grid, x - 1, y, val);
+        countArea(grid, x, y + 1, val);
+        countArea(grid, x, y - 1, val);
+    }
+
+    int maxAreaOfIsland(vector<vector<int>>& grid) {
+        m = grid.size();
+        n = grid[0].size();
+        int maxArea = 0;
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                if (grid[i][j] == 1) {
+                    int val = 0;
+                    countArea(grid, i, j, val);
+                    maxArea = max(maxArea, val);
+                }
+            }
+        }
+        return maxArea;
+    }
+};