var arr = [];
$("input").each(function(){
var value = $(this).val();
if (arr.indexOf(value) == -1)
arr.push(value);
else
$(this).addClass("duplicate");
});
.duplicate {
border: 1px solid red;
color: red;
}
<table>
<tr><td><input value="one"></td></tr>
<tr><td><input value="two"></td></tr>
<tr><td><input value="one"></td></tr>
<tr><td><input value="nine"></td></tr>
<tr><td><input value="four"></td></tr>
<tr><td><input value="four"></td></tr>
</table>