leetcode--Algorithm--Array

2017-12-04  15:33:07

LeetCode 刷题准备面试

分类刷题：Start -- Array

"need a more efficient way to check if the complements exists in the way.if the complements exists, we need to look up its index. the best way to maintain a mapping of each elements int the array to its index?

-- A hash table. "

    public int[] twoSum(int[] nums, int target){
        Map<Integer, Integer> map = new HashMap<>();
        for(int index = 0; index < nums.length; index++)
        {
            map.put(nums[index],index);
        }

        for(int i = 0; i < nums.length; i++)
        {
            int complement = target - nums[i];

            //precondition1: in the second iteration we check if each elements`s
            //complement (target - nums[i]) exists in the table.
            //precondition2: the complement must not be nums[i] itself

            if(map.containsKey(nums[i]) && map.get(nums[i]) != i){
                return new int[] {i, map.get(complement)};
            }
        }

        throw new IllegalArgumentException("No two sum solution");
    }