1. Two Sum

时间:2019-07-11
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一. 链接和题目简单介绍

      链接:[LeetCode-01]-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].    



二. 分析


  用哈希map 应该会快点

 

三. 代码

 Java:

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

 

  JS:

const twoSum = function(nums, target) {
    const comp = {};
    for(let i=0; i<nums.length; i++){
        if(comp[nums[i] ]>=0){
            return [ comp[nums[i] ] , i]
        }
        comp[target-nums[i]] = i
    }
};

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