LeetCode學習

1. Two Sum

• Total Accepted: 264908
• Total Submissions: 1053667
• Difficulty: Easy

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.

Example:

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

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

第一種方法：

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        int []a=new int[2];
        for(int i=0;i<num.size()-1;i++){
            for(int j=i+1;j<num.size();j++){
                if(nums[i]+nums[j]==target){
                    a[0]=num[i];
                    a[1]=num[j]
                    return a;
                }
            }
        }
    }
}

提示：

第二種方法：

public class Solution {  
    public int[] twoSum(int[] nums, int target) {  
        int[] a=new int[2];
        HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
        
        for(int i = 0; i<nums.length; i++)
        {
            if(hm.containsKey(target - nums[i]))
            {
                a[1] = i+1;
                a[0] = hm.get(target-nums[i])+1;   
                return a;   
            }else
            {
                 hm.put(nums[i],i);
            }
        }
        return a;  
    }
     
}