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].
这道题是最经典的一道题，任何学过算法的同学接触的第一道题就是这道。用一个hash table去存，key是这个index对应的数，value是这个index。
class Solution {
public int[] twoSum(int[] nums, int target) {
Map<Integer, Integer> map = new HashMap<>();
int i;
for (i = 0; i < nums.length; i++) {
if (map.containsKey(target - nums[i])) {
return new int[]{map.get(target - nums[i]), i};
}
map.put(nums[i], i);
}
return new int[0];
}
}