diff --git a/include/World.h b/include/World.h
index 4df0a22..ee8bc60 100644
--- a/include/World.h
+++ b/include/World.h
@@ -1,56 +1,51 @@
 #pragma once
 
 #include <vector>
+#include <memory>
+
+class Robot;
 
 /* A 3-D grid world where robots mine positive-value blocks and trigger effects. */
 class World {
   public:
     explicit World ( int x = 5, int y = 5, int z = 10 );
 
-    /* Return the value at (x, y, z).
-       Throws std::out_of_range for invalid coordinates.
-       Complexity: O(1) */
-    int getValue ( int x, int y, int z ) const;
-
-    /* Set the value at (x, y, z).
-       Throws std::out_of_range for invalid coordinates.
-       Complexity: O(1) */
-    void setValue ( int x, int y, int z, int value );
-
-    /* Return the highest z in column (x, y) containing a positive value.
-       Returns -1 if no minable block exists in the column.
-       Complexity: O(sizeZ) */
-    int getSurfaceLevel ( int x, int y ) const;
-
-    /* Mine the current surface block at (x, y), set it to 0, and return its value.
-       Returns 0 if the column has no minable surface.
-       Complexity: O(sizeZ) */
-    int mine ( int x, int y );
-
-    /* Print a 2-D surface view of the world with optional robot markers.
-       Pass default coordinates (-1, -1) to omit a robot marker.
-       Complexity: O(sizeX * sizeY * sizeZ) */
-    void display ( int p1x = -1, int p1y = -1, int p2x = -1, int p2y = -1 ) const;
-
     int getSizeX () const { return _sizeX; }
     int getSizeY () const { return _sizeY; }
     int getSizeZ () const { return _sizeZ; }
 
-    /* Rearrange each column by applying a random operation
-       (shuffle, ascending sort, or descending sort) to non-zero entries.
-       Complexity: O(sizeX * sizeY * sizeZ log sizeZ) */
+    int getValue ( int x, int y, int z ) const;
+    void setValue ( int x, int y, int z, int value );
+    void setColumn ( int x, int y, const std::vector<int>& values );
+    std::vector<int> getColumn ( int x, int y ) const;
+    void clear ();
+
+    int getSurfaceLevel ( int x, int y ) const;
+    int getSurfaceValue ( int x, int y ) const;
+    bool hasPositiveValues () const;
+    int remainingPositiveSum () const;
+
+
+    int mine ( int x, int y );
+    int checkEffects ( int x, int y );
+    int mineAllPositive ( int x, int y );
+
+    double posiveAverage ( int x, int y ) const;
+    int topPositiveSum ( int x, int y, int blocks ) const;
+    void sortPositiveValuesInColumnAscending ( int x, int y );
     void rearrange ();
 
-    /* Find and consume one negative effect value in column (x, y).
-       Returns 0 if no effect exists.
-       Complexity: O(sizeZ) */
-    int checkEffects ( int x, int y );
+    void display () const;
+    void display ( const std::vector<std::unique_ptr<Robot>>& robots) const;
 
   private:
-    int _sizeX, _sizeY, _sizeZ;
-    std::vector<std::vector<std::vector<int>>> _grid;
+    int sizeX_ = 5;
+    int sizeY_ = 5;
+    int sizeZ_ = 10;
+    std::vector<std::vector<std::vector<int>>> grid_;
+
+    void init();
+    void validateXY ( int x, int y ) const;
+    void validateZ ( int z ) const;
 
-    /* Initialize the grid with random positive values and occasional effects.
-       Complexity: O(sizeX * sizeY * sizeZ) */
-    void init ();
 };
diff --git a/src/World.cpp b/src/World.cpp
index 789a2f8..6a66dc9 100644
--- a/src/World.cpp
+++ b/src/World.cpp
@@ -1,4 +1,5 @@
 #include "../include/World.h"
+#include "../include/Robot.h"
 
 #include <algorithm>
 #include <iomanip>
@@ -9,8 +10,9 @@
 /* Construct a 3D grid world and initialize all cells.
    Complexity: O(x × y × z) */
 World::World ( int x, int y, int z )
-    : _sizeX ( x ), _sizeY ( y ), _sizeZ ( z ),
-      _grid ( x, std::vector<std::vector<int>> ( y, std::vector<int> ( z, 0 ) ) ) {
+    : sizeX_ ( x ), sizeY_ ( y ), sizeZ_ ( z ),
+      grid_ ( x, std::vector<std::vector<int>> ( y ) ) {
+          if ( x <= 0 || y <= 0 || z <= 0 ) throw std::invalid_argument( "World dimensions must be positive.");
     init();
 }
 
@@ -21,61 +23,124 @@ void World::init () {
     std::mt19937 rng ( std::random_device {}() );
     std::uniform_int_distribution<int> valueDist ( 1, 9 );
     std::uniform_int_distribution<int> effectChance ( 0, 9 );
-    std::uniform_int_distribution<int> effectType ( -3, -1 );
+    std::uniform_int_distribution<int> effectDist ( 3, 1 );
 
-    for ( int x = 0; x < _sizeX; ++x ) {
-        for ( int y = 0; y < _sizeY; ++y ) {
-            for ( int z = 0; z < _sizeZ; ++z ) {
-                _grid[ x ][ y ][ z ] = ( effectChance ( rng ) == 1 ) ? effectType ( rng ) : valueDist ( rng );
+    for ( int x = 0; x < sizeX_; ++x ) {
+        for ( int y = 0; y < sizeY_; ++y ) {
+            auto& col = grid_[x][y];
+            col.clear();
+            col.reserve ( sizeZ_ );
+            for ( int z = 0; z < sizeZ_; ++z ) {
+                col.push_back( effectChance (rng ) == 1 ? -effectDist (rng ) : valueDist (rng ) );
             }
         }
     }
 }
 
-/* Return the value at (x, y, z), throwing on invalid coordinates.
-   Complexity: O(1) */
+/* validate coordinates  */
+void World::validateXY ( int x, int y ) const {
+   if ( x < 0 || x >= sizeX_ || y < 0 || y >= sizeY_ ) throw std::out_of_range( "World coordinate out of range." );
+}
+
+void World::validateZ( int z ) const {
+    if ( z < 0 || z >= sizeZ_ ) throw std::out_of_range ( "World depth out of range." );
+}
+
+/* public API */
 int World::getValue ( int x, int y, int z ) const {
-    if ( x < 0 || x >= _sizeX || y < 0 || y >= _sizeY || z < 0 || z >= _sizeZ ) {
-        throw std::out_of_range ( "Coordinates out of bounds" );
-    }
-    return _grid[ x ][ y ][ z ];
+    validateXY( x, y );
+    validateZ ( z );
+    const auto& col = grid_[x][y];
+    return z < static_cast<int> ( col.size() ) ? col[z] : 0;
 }
 
-/* Set the value at (x, y, z), throwing on invalid coordinates.
-   Complexity: O(1) */
 void World::setValue ( int x, int y, int z, int value ) {
-    if ( x < 0 || x >= _sizeX || y < 0 || y >= _sizeY || z < 0 || z >= _sizeZ ) {
-        throw std::out_of_range ( "Coordinates out of bounds" );
-    }
-    _grid[ x ][ y ][ z ] = value;
-}
-
-/* Return the highest z with a positive value in column (x, y).
-   Negative effect cells are ignored for mining surface purposes.
-   Complexity: O(z) */
-int World::getSurfaceLevel ( int x, int y ) const {
-    for ( int z = _sizeZ - 1; z >= 0; --z ) {
-        if ( _grid[ x ][ y ][ z ] > 0 ) {
-            return z;
+    validateXY( x, y );
+    validateZ( z );
+    auto& col = grid_[x][y];
+    if ( value == 0 ) {
+        if ( z < static_cast<int> (col.size ())) {
+            col.erase( col.begin() + z );
+            return;
+        }
+        if ( z > static_cast<int> ( col.size())) {
+            throw std::logic_error( "setValue would result in holes, use SetColumn." );
+        }
+        if ( z == static_cast<int> ( col.size() ) ) {
+            col.push_back( value );
+        } else {
+            col[z] = value;
         }
     }
-    return -1;
 }
 
-/* Mine one topmost positive block from column (x, y) and return its value.
-   Returns 0 when the column has no mineable block.
-   Complexity: O(z) */
-int World::mine ( int x, int y ) {
-    const int z = getSurfaceLevel ( x, y );
-    if ( z == -1 ) {
-        return 0;
+void World::setColumn( int x, int y, const std::vector<int>& value ) {
+    validateXY( x, y );
+    if ( static_cast<int> ( value.size()) > sizeZ_ ) {
+        throw std::out_of_range( "Column is too deep." );
     }
+    grid_[x][y] = value;
+}
 
-    const int value = _grid[ x ][ y ][ z ];
-    if ( value > 0 ) {
-        _grid[ x ][ y ][ z ] = 0;
+std::vector<int> World::getColumn( int x, int y ) const {
+    validateXY( x, y );
+    return grid_[x][y];
+}
+
+void World::clear() {
+    for ( auto& row : grid_ ) {
+        for ( auto& col : row ) {
+            col.clear();
+        }
     }
-    return value;
+}
+
+int World::getSurfaceLevel ( int x, int y ) const {
+    validateXY( x, y );
+    const auto& col = grid_[x][y];
+    return col.empty() ? -1 : static_cast<int> ( col.size()) -1;
+}
+
+int World::getSurfaceValue( int x, int y ) const {
+    validateXY( x, y );
+    const auto& col = grid_[x][y];
+    return col.empty() ? 0 : col.back();
+}
+
+int World::remainingPositiveSum() const {
+    int sum = 0;
+    for ( const auto& row : grid_ ) {
+        for ( const auto& col : row ) {
+            for ( int v : col ) {
+                if ( v > 0 ) sum += v;
+            }
+        }
+    }
+    return sum;
+}
+
+bool World::hasPositiveValues() const {
+    return remainingPositiveSum() > 0;
+}
+
+int World::checkEffects ( int x, int y ) {
+    validateXY( x, y );
+    auto& col = grid_[x][y];
+    if ( !col.empty() && col.back() < 0 ) {
+        int effect = col.back();
+        col.pop_back();
+        return effect;
+    }
+    return 0;
+}
+
+int World::mine ( int x, int y ) {
+    validateXY( x, y );
+    auto& col = grid_[x][y];
+    if ( col.empty() ) return 0;
+    int value = col.back();
+    col.pop_back();
+    return value > 0 ? value : 0;
 }
 
 /* Print a 2D surface view with optional player/computer markers.
@@ -89,16 +154,16 @@ void World::display ( int p1x, int p1y, int p2x, int p2y ) const {
     }
 
     std::cout << "   ";
-    for ( int y = 0; y < _sizeY; ++y ) {
+    for ( int y = 0; y < sizeY_; ++y ) {
         std::cout << std::setw ( 4 ) << y;
     }
     std::cout << "\n";
 
-    for ( int x = 0; x < _sizeX; ++x ) {
+    for ( int x = 0; x < sizeX_; ++x ) {
         std::cout << std::setw ( 2 ) << x << " ";
-        for ( int y = 0; y < _sizeY; ++y ) {
+        for ( int y = 0; y < sizeY_; ++y ) {
             const int surface = getSurfaceLevel ( x, y );
-            const int val = ( surface >= 0 ? _grid[ x ][ y ][ surface ] : 0 );
+            const int val = ( surface >= 0 ? grid_[ x ][ y ][ surface ] : 0 );
             const bool hasP1 = ( x == p1x && y == p1y );
             const bool hasP2 = ( x == p2x && y == p2y );
 
@@ -125,14 +190,14 @@ void World::rearrange () {
     std::mt19937 rng ( std::random_device {}() );
     std::uniform_int_distribution<int> opDist ( 0, 2 );
 
-    for ( int x = 0; x < _sizeX; ++x ) {
-        for ( int y = 0; y < _sizeY; ++y ) {
+    for ( int x = 0; x < sizeX_; ++x ) {
+        for ( int y = 0; y < sizeY_; ++y ) {
             std::vector<int> values;
             std::vector<int> positions;
 
-            for ( int z = 0; z < _sizeZ; ++z ) {
-                if ( _grid[ x ][ y ][ z ] > 0 ) {  // only minable blocks; effect cells stay in place
-                    values.push_back ( _grid[ x ][ y ][ z ] );
+            for ( int z = 0; z < sizeZ_; ++z ) {
+                if ( grid_[ x ][ y ][ z ] > 0 ) {  // only minable blocks; effect cells stay in place
+                    values.push_back ( grid_[ x ][ y ][ z ] );
                     positions.push_back ( z );
                 }
             }
@@ -150,7 +215,7 @@ void World::rearrange () {
             }
 
             for ( std::size_t i = 0; i < positions.size(); ++i ) {
-                _grid[ x ][ y ][ positions[ i ] ] = values[ i ];
+                grid_[ x ][ y ][ positions[ i ] ] = values[ i ];
             }
         }
     }
@@ -159,15 +224,3 @@ void World::rearrange () {
 /* Find and consume the first negative effect value in column (x, y).
    Returns 0 when no effect exists in that column.
    Complexity: O(z) */
-int World::checkEffects ( int x, int y ) {
-    auto &col = _grid[ x ][ y ];
-    auto it = std::find_if ( col.begin(), col.end(), [] ( int v ) { return v < 0; } );
-
-    if ( it == col.end() ) {
-        return 0;
-    }
-
-    const int effect = *it;
-    *it = 0;
-    return effect;
-}