I have one scenario like Year in integer and week in String and wanted to calculate the YTD.. how to do this.?

In Tableau, the relative date filter enables flexible analysis of time periods. Sometimes, however, you might want to see both year-to-date (YTD) and month-to-date (MTD) values for a particular measure on the same view. To accomplish this task, you can create date calculations.

Create a calculated column which replaces week from string to integer and make use this in another calculation for YTD.

YTD:

MTD: