leetcode#1-Two Sum-java

KateGoGo

于 2017-09-10 11:39:33 发布

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分类专栏：算法oj 文章标签： twosum leetcode

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本文介绍了一种解决'两数之和'问题的有效算法。该算法通过使用哈希表来快速查找目标值对应的配对元素，从而实现快速求解。输入为整数数组和目标值，输出为数组中两个数的下标，这两个数相加等于目标值。

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题目：

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].

解法：

public class TwoSum_1 {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer,Integer> map = new HashMap<Integer,Integer>();
        int [] a = {0,0};
        for(int i = 0;i<nums.length;i++){
            if(map.containsKey(target-nums[i])){
                a[0] = map.get(target-nums[i]);
                a[1] = i;
            }else {
                map.put(nums[i], i);
            }
        }
        return a;
    }

    public static void main(String[] args){
        TwoSum_1 ts = new TwoSum_1();
    }
}