1. Two Sum
Tags: ‘Array’, ‘Hash Table’
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
class Solution {
public int[] twoSum(int[] nums, int target) {
Map<Integer, Integer> map = new HashMap<>(); // map number to index
int[] result = new int[2];
for (int i = 0; i < nums.length; i++) {
int num = nums[i];
if (map.containsKey(target - num)){
result[0] = map.get(target - num);
result[1] = i;
return result;
} else {
map.put(num, i);
}
}
return new int[]{-1, -1};
}
}