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2021-01-20
1. Two Sum
Question:
Given an array of integers nums
and an integer target
, return indices of the two numbers such that they add up to target
.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
You can return the answer in any order.
Example 1:
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:
Input: nums = [3,2,4], target = 6
Output: [1,2]
Example 3:
Input: nums = [3,3], target = 6
Output: [0,1]
Constraints:
2 <= nums.length <= 103
-109 <= nums[i] <= 109
-109 <= target <= 109
- Only one valid answer exists.
Solution:
Using the hashmap to record the (value, index). If we can find the target value from the hashmap, return the result.
class Solution {
public int[] twoSum(int[] nums, int target) {
HashMap<Integer, Integer> map = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
int curr = nums[i];
if (map.get(target - curr) != null) {
return new int[]{i, map.get(target - curr)};
}
map.put(curr, i);
}
return new int[]{};
}
}