// Assume a lava flow is entering (row,col) from an elevation of "inElevation".
// If (row,col) has a greater elevation, the lava flow is stopped.  
// Otherwise, (row,col) gets scorched and lava may flow up, down, left, and right from this cell.
// Every "scorched" cell gets set to an elevation of zero.
void  doLavaFlow(int **map, int numRows, int numCols, int row, int col, int inElevation)
{
    // If this location is out of bounds, we've gone off edge, so stop
    if (!inBounds(numRows, numCols, row, col)) {
        return;
    }

    int thisElevation = map[row][col];

    // There is lava entering (row,col) at the given elevation.
    // BUT if elevation of current cell is higher, this cell stops the lava
    if (thisElevation > inElevation) {
        return; // we stopped the lava!
    }

    // OR if this cell is already scorched, no need to handle this one again
    if (thisElevation == 0) {
        return; // already scorched
    }


    // Okay, this cell is scorched // mark with zero
    map[row][col] = 0;

    // Lava can flow from this point, at this elevation, to four surrounding areas.
    doLavaFlow(map, numRows, numCols, row-1, col  , thisElevation);
    doLavaFlow(map, numRows, numCols, row+1, col  , thisElevation);
    doLavaFlow(map, numRows, numCols, row  , col-1, thisElevation);
    doLavaFlow(map, numRows, numCols, row  , col+1, thisElevation);
    return;
}