0401-0410 401. Binary Watch $\star$ 402. Remove K Digits $\star\star$ 403. Frog Jump $\star\star\star$ 404. Sum of Left Leaves $\star$ 405. Convert a Number to Hexadecimal $\star$ 406. Queue Reconstruction by Height $\star\star$ 407. Trapping Rain Water II $\star\star\star$ 408. Valid Word Abbreviation $\star$ 409. Longest Palindrome $\star$ 410. Split Array Largest Sum $\star\star\star$