苦思冥想

kǔsīmíngxiǎng
(idiom) to think deeply; to rack one's brains

CEDICT

to think long and hard

Wiktionary

尽心地思索和想像

維基詞典

Entry Composition

1 苦思 kǔsī
  1. to think hard
  2. bitter thoughts
  3. to pour out one's sufferings
2 冥想 míngxiǎng
  1. to meditate
  2. meditation