Google Script check duplication item

check_duplication_item.gs

function onOpen() {
  var sheet = SpreadsheetApp.getActiveSpreadsheet();
  var entries = [{name : "Check Duplicates",functionName : "checkDuplicates"}];
  sheet.addMenu("Scripts", entries);
};

function checkDuplicates() {
  var sheet = SpreadsheetApp.getActiveSheet();
  //var dataRange = sheet.getDataRange();
  var dataRange = sheet.getRange("A:A"); // Set Any Range
  var data = dataRange.getValues();
  var numRows = data.length;
  var numColumns = data[0].length;

  var formats = [];
  var values = [];
  for (var i = 0; i < numRows; i++) {
    formats[i] = [];
    for (var j = 0; j < numColumns; j++) {
      formats[i][j] = 'WHITE';
      if (data[i][j] != '') {
        values.push([data[i][j], i, j]);
      }
    }
  }
  var numValues = values.length;
  
  for (var k = 0 ; k < numValues - 1; k++) {
    if (formats[values[k][1]][values[k][2]] == 'WHITE') {
      for (var l = k + 1; l < numValues; l++) {
        if (values[k][0] == values[l][0]) {
          formats[values[k][1]][values[k][2]] = 'RED';
          formats[values[l][1]][values[l][2]] = 'RED';
        }
      }
    }
  }
    
  dataRange.setBackgroundColors(formats);
}