Leetcode 1 -- Two Sum

Leetcode 1 -- Two Sum

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.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

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解法1：主要思想是运用哈希表，问题假设只有唯一答案，扫描一遍即可，哈希表中存储target与当前元素的差值，以及当前元素的下标。如匹配，返回当前下标和哈希表中下标，如不匹配存入哈希表。

public class Solution {
public int[] twoSum(int[] nums, int target) {
int[] result = new int[2];
Map<Integer,Integer> map = new HashMap<>();

for(int i = 0 ; i < nums.length ; i++){
if(map.containsKey(nums[i])){
result[0] = map.get(nums[i]);
result[1] = i;
return result;
}else{
map.put(target-nums[i],i);
}
}
return result;
}
}