Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
Example:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
Solution
- 使用一个
hashmap来记录<num,index>的映射 - 遍历数组
- 查找map中是否存在
key = target-num - 存在，直接返回结果
- 不存在，将本次的
<num,index>加入map
- 查找map中是否存在
Code (Java)
public int[] twoSum(int[] nums, int target) {
Map<Integer,Integer> indexMapping = new HashMap();
for(int i = 0; i < nums.length; i++) {
int key = target - nums[i];
if(indexMapping.containsKey(key)) {
int index = indexMapping.get(key);
return new int []{index, i};
}
indexMapping.put(nums[i],i);
}
return new int[]{-1,-1};
}
