function findDuplicates() {
// List the columns you want to check by number (A = 1)
var CHECK_COLUMNS = [1];
// Get the active sheet and info about it
var sourceSheet = SpreadsheetApp.getActiveSheet();
var numRows = sourceSheet.getLastRow();
var numCols = sourceSheet.getLastColumn();
// Create the temporary working sheet
var ss = SpreadsheetApp.getActiveSpreadsheet();
var newSheet = ss.insertSheet("FindDupes");
// Copy the desired rows to the FindDupes sheet
for (var i = 0; i < CHECK_COLUMNS.length; i++) {
var sourceRange = sourceSheet.getRange(1,CHECK_COLUMNS[i],numRows);
var nextCol = newSheet.getLastColumn() + 1;
sourceRange.copyTo(newSheet.getRange(1,nextCol,numRows));
}
// Find duplicates in the FindDupes sheet and color them in the main sheet
var dupes = false;
var data = newSheet.getDataRange().getValues();
for (i = 1; i < data.length - 1; i++) {
for (j = i+1; j < data.length; j++) {
if (data[i].join() == data[j].join()) {
dupes = true;
sourceSheet.getRange(i+1,1,1,numCols).setBackground("red");
sourceSheet.getRange(j+1,1,1,numCols).setBackground("red");
}
}
}
// Remove the FindDupes temporary sheet
ss.deleteSheet(newSheet);
// Alert the user with the results
if (dupes) {
Browser.msgBox("Possible duplicate(s) found and colored red.");
} else {
Browser.msgBox("No duplicates found.");
}
};