Google Apps Script, number of people scheduled

People Busy, Google Spreadsheet

function peopleBusy(people, startRow, startCol, endRow, endCol) {
  startRow = startRow || 2;
  startCol = startCol || 2;
  endRow = endRow || 40;
  endCol = endCol || 9;
  
  people = people.split(",");
  var ss = SpreadsheetApp.getActiveSpreadsheet(); 
  
  var n, i, j;
  var sheet, range;
  numRows = endRow - startRow + 1;
  numCols = endCol - startCol + 1;
  
  var busy = new Array(numRows);
  for (i = 0; i < numRows; i++) {
    busy[i] = new Array(numCols);
    for (j = 0; j < numCols; j++) {
      busy[i][j] = "";
    }
  }
  
  var lock = LockService.getPublicLock();
  lock.waitLock(180000);
  
  for (n = 0; n < people.length; n++) {
    person = people[n].trim();
    sheet = ss.getSheetByName(person);
    vals = sheet.getRange(startRow, startCol, numRows, numCols).getValues();
    
    for (i = 0; i < numRows; i++) {
      for (j = 0; j < numCols; j++) {
        if (vals[i][j] != "") {
          busy[i][j] += person.substring(0,1);
        }
      }
    }   
  }
  lock.releaseLock();
  
  for (i = 0; i < numRows; i++) {
    for (j = 0; j < numCols; j++) {
      if (busy[i][j] != "") {
        busy[i][j] = "x" + busy[i][j];
      }
    }
  }
  return busy;
}