Description
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
Two-pointer, O(n ^ 2), S(1)
class Solution {
public int[] twoSum(int[] nums, int target) {
for (int i = 0; i < nums.length - 1; ++i) {
for (int j = i + 1; j < nums.length; ++j) {
if (nums[i] + nums[j] == target) {
return new int[] {i, j};
}
}
}
return new int[] {-1, -1};
}
}
HashMap, O(n), S(n)
class Solution {
public int[] twoSum(int[] nums, int target) {
Map<Integer, Integer> val2Idx = new HashMap<>();
for (int i = 0; i < nums.length; ++i) {
int pair = target - nums[i];
if (val2Idx.containsKey(pair)) {
return new int[] {val2Idx.get(pair), i};
}
val2Idx.put(nums[i], i);
}
return new int[] {-1, -1};
}
}
