BE Study

1. Two Sum: find a pair with specific sum   class Solution : def twoSum ( self , nums : List [ int ] , target : int ) - > List [ int ] : numMap = { } n = len ( nums ) # Build the hash table for i in range ( n ) : numMap [ nums [ i ] ] = i # Find the complement for i in range ( n ) : complement = target - nums [ i ] if complement in numMap and numMap [ complement ] != i : return [ i , numMap [ complement ] ] return [ ] # No solution found You might wonder how does the code deals with duplicates. As you can see, in the iteration of building the hash table, always the latter(with bigger index) will be saved in the hash table. In the latter iteration finding the complement, the former one(with smaller index) always goes through the iteration earlier, so the [i, numMap[complement]] can return two different indexes, carrying duplicate...