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This article mainly introduces java how to achieve the sum of two numbers, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

Topic description

Given an array of integers nums and a target value target, please find the two integers in the array that are the target values and return their array subscript.

You can assume that each input corresponds to only one answer. However, you cannot reuse the same elements in this array.

Example:

Given nums = [2,7,11,15], target = 9

Because nums [0] + nums [1] = 2 + 7 = 9, return to the solution of [0,1]

Tags: hash mapping

The problem itself can be easily solved by violent traversal, and the time complexity is O (N2).

Since the time complexity of hash search is O (1), the hash container map can be used to reduce the time complexity.

The traversal array nums,i is the current subscript, and each value determines whether the key value of target-nums [I] exists in map.

If it exists, two values are found. If it does not exist, the current (nums [I], I) is stored in map, and continue traversing until it is found.

Throw an exception if there is no result in the end

Time complexity: O (n)

Code class Solution {public int [] twoSum (int [] nums, int target) {Map map = new HashMap (); for (int 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); } throw new IllegalArgumentException("No two sum solution"); }}画解

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