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Author: MathProgrammer

2020/Div 3/634 Div 3/Programs/Robots on a Grid.cpp

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+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+const int MAX_L = 25;
+
+int rows, columns;
+vector <string> colour;
+vector <string> S;
+vector <vector <int> > step(MAX_L);
+vector <int> visited;
+
+int label(int x, int y)
+{
+    return x*columns + y;
+}
+
+int is_bit_set(int n, int bit)
+{
+    return ((n&(1 << bit)) != 0);
+}
+
+int get_next(int x, int y)
+{
+    switch(S[x][y])
+    {
+        case 'U' : return label(x - 1, y);
+        case 'R' : return label(x, y + 1);
+        case 'L' : return label(x, y - 1);
+        case 'D' : return label(x + 1, y);
+    }
+    
+    return 0;
+}
+
+void dfs(int v)
+{
+    if(visited[v])
+    {
+        return;
+    }
+    
+    visited[v] = true;
+    
+    int x = v/columns, y = v%columns;
+    
+    int next = get_next(x, y);
+    //cout << "At " << v << " " << x << "," << y << " Next = " << next << "\n";
+    step[0][v] = next;
+    
+    dfs(next);
+}
+
+void solve()
+{
+    cin >> rows >> columns;
+    
+    colour.resize(rows);
+    for(int i = 0; i < rows; i++)
+    {
+        cin >> colour[i];
+    }
+    
+    S.resize(rows);
+    for(int i = 0; i < rows; i++)
+    {
+        cin >> S[i];
+    }
+    
+    visited.resize(rows*columns, false);
+    for(int i = 0; i < rows*columns; i++)
+    {
+        visited[i] = false;
+    }
+    
+    for(int i = 0; i < MAX_L; i++)
+    {
+        step[i].resize(rows*columns);
+    }
+    
+    for(int v = 0; v < rows*columns; v++)
+    {
+        if(!visited[v])
+        {
+            dfs(v);
+        }
+    }
+    
+    for(int l = 1; l < MAX_L; l++)
+    {
+        for(int i = 0; i < rows*columns; i++)
+        {
+            int previous_step = step[l - 1][i];
+            
+            //cout << "L = " << l << "Start at " << i/columns << "," << i%columns << " previous = " << previous_step/columns << "," << previous_step%columns <<" and finish at " << step[l - 1][previous_step]/columns << " " << step[l - 1][previous_step]%columns << "\n";
+            
+            step[l][i] = step[l - 1][previous_step];
+        }
+    }
+    
+    vector <int> black_starts(rows*columns);
+    vector <int> white_starts(rows*columns);
+    int total_steps = rows*columns;
+    for(int i = 0; i < rows*columns; i++)
+    {
+        int finish = i;
+        
+        for(int bit = MAX_L - 1; bit >= 0; bit--)
+        {
+            if(is_bit_set(total_steps, bit))
+            {
+                finish = step[bit][finish];
+            }
+        }
+        
+        const char BLACK = '0', WHITE = '1';
+        int start_x = i/columns, start_y = i%columns;
+        if(colour[start_x][start_y] == BLACK)
+        {
+            black_starts[finish]++;
+        }
+        else
+        {
+            white_starts[finish]++;
+        }
+        
+        //cout << "Start at " << start_x << "," << start_y << " and finish at " << finish/columns << " " << finish%columns << "\n";
+    }
+    
+    int total = 0, black = 0;
+    for(int i = 0; i < rows; i++)
+    {
+        for(int j = 0; j < columns; j++)
+        {
+            if(black_starts[label(i, j)] > 0)
+            {
+                total++;
+                black++;
+            }
+            else if(white_starts[label(i, j)] > 0)
+            {
+                total++;
+            }
+        }
+    }
+    
+    cout << total << " " << black << "\n";
+}
+
+int main()
+{
+    int no_of_test_cases;
+    cin >> no_of_test_cases;
+    
+    while(no_of_test_cases--)
+        solve();
+    
+    return 0;
+}