[leetcode] 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, 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].

• 暴力

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  class { public int[] twoSum(int[] nums, int target) { for (int i = 0; i < nums.length; i++) { for (int j = i + 1; j < nums.length; j++) { if (nums[i] + nums[j] == target) { return new int[]{i, j}; } } } throw new IllegalArgumentException("No two sum solution"); } }

• HashMap

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  public int[] twoSum(int[] nums, int target) { HashMap<Integer, Integer> map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { if (map.containsKey(target - nums[i])) { return new int[]{i, map.get(target - nums[i])}; } map.put(nums[i],i); } throw new IllegalArgumentException("No two sum solution"); }