TwoSum问题

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].

我的算法

public int[] solution(int[] nums,int target){
		Map<Integer,Integer> map=new HashMap<Integer,Integer>();
		int[] res=new int[2];
		for(int i=0;i<nums.length;i++){
			if(map.containsKey(target-nums[i])){
				res[0]=i;
				res[1]=map.get(target-nums[i]);
			}
			map.put(nums[i], i);
		}
		return res;
	}

网上还有一种不使用HashMap的方法，但是当数组中有重复的数出现时可能会出现数组越界问题

public int[] solution2(int[] nums,int target){
		int[] nums_sorted=new int[nums.length];
		System.arraycopy(nums,0, nums_sorted, 0, nums.length);
		
		Arrays.sort(nums_sorted);
		
		int start=0;
		int end=nums_sorted.length;
		while(start<end){
			while(nums_sorted[start]+nums_sorted[--end]>target);
			if(nums_sorted[start]+nums_sorted[end]==target)
				break;
			while(nums_sorted[++start]+nums_sorted[end]<target);
			if(nums_sorted[end]+nums_sorted[start]==target)
				break;
		}
		
		int[] res=new int[2];
		int index=0;
		int a=nums_sorted[start];
		int b=nums_sorted[end];
		for(int i=0;i<nums.length;i++){
			if(nums[i]==a||nums[i]==b)
				res[index++]=i;
		}
		return res;
	}

加油！