枉费

wǎng fèi xīn lì

枉费心力

rack one's brains in vain

wǎng fèi yī fān gōng fu

枉费一番工夫

waste time and energy

wǎng fèi jīn qián

枉费金钱

throw away good money for nothing

wǎng fèi fù mǔ de yī piàn kǔ xīn

枉费父母的一片苦心

a waste of one's parents' efforts

wǎng fèi kǒu shé

枉费口舌

be a mere waste of breath

jǐng fāng diào chá zhè qǐ xiōng shā àn shí fāng xiàng bù duì tóu wǎng fèi le sān gè yuè de shí jiān

警方调查这起凶杀案时方向不对头，枉费了三个月的时间。

The police spent three months barking up the wrong tree on the murder investigation.