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Author: assassint2017

Rotting Oranges/Rotting_Oranges.cpp

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+// 基本思路是使用广度优先搜索进行加速
+// Runtime: 4 ms, faster than 94.02% of C++ online submissions for Rotting Oranges.
+// Memory Usage: 9.1 MB, less than 81.25% of C++ online submissions for Rotting Oranges.
+
+class Solution 
+{
+public:
+    int orangesRotting(vector<vector<int>>& grid) 
+    {
+        // 边界条件处理
+        int row = grid.size();
+        if (row == 0) return -1;
+        
+        int col = grid[0].size();
+        if (col == 0) return -1;
+        
+        // 首先纳入已经坏掉的橘子的坐标
+        int numOfFresh = 0;
+        int numOfRotten = 0;
+        queue<pair<int, int>> poss;
+        for (int i = 0; i < row; ++i)
+        {
+            for (int j = 0; j < col; ++j)
+            {
+                if (grid[i][j] == 1)
+                {
+                    ++numOfFresh;
+                }
+                
+                if (grid[i][j] == 2)
+                {
+                    ++numOfRotten;
+                    poss.push(make_pair(i, j));
+                }
+            }
+        }
+        
+        // 边界条件处理
+        if (numOfFresh == 0 && numOfRotten == 0)
+            return 0;
+        if (numOfFresh == 0 && numOfRotten != 0)
+            return 0;
+        if (numOfFresh != 0 && numOfRotten == 0)
+            return -1;
+        
+        // BFS
+        int layer = 0;
+        int offsetx[] = {-1, 1, 0, 0};
+        int offsety[] = {0, 0, -1, 1};
+        while (!poss.empty())
+        {
+            for (int i = poss.size(); i > 0; --i)
+            {
+                auto pos = poss.front();
+                poss.pop(); 
+                
+                for (int j = 0; j < 4; ++j)
+                {
+                    int newx = pos.first + offsetx[j];
+                    int newy = pos.second + offsety[j];
+                    if (newx >= 0 && newx < row && newy >= 0 && newy < col && grid[newx][newy] == 1)
+                    {
+                        grid[newx][newy] = 2;
+                        poss.push(make_pair(newx, newy));
+                        
+                        --numOfFresh;
+                        ++numOfRotten;
+                    }
+                }
+            }
+            ++layer;
+        }
+        
+        if (numOfFresh == 0)
+            return layer - 1;
+        else
+            return -1;
+    }
+};