Given an array of integers, return indices of the two numbers such that they add up to a specific ta

问题是要从数组中找到两个数据，使得两数之和等于目标值，输出该两数的下标（从0开始）

方法一:

public static int[] twoSum_2(int[] num,int target ) {
		int low ,high;
		int temp;
		for(int i = 0; i< num.length; i++){
			low = i;
			temp = target- num[i];
			for(int j =i+1; j< num.length; j++){
				if(temp == num[j]){
					high = j;
					return new int[]{low,high};
				}
			}
			
			
		}
		return null;
	}

 方法二:用hashmap减少查找时间

import java.util.HashMap;
import java.util.Scanner;

import javax.swing.text.NumberFormatter;


public class Solution {
	public static int[] twoSum(int[] num,int target ) {
		final HashMap myMap = new HashMap();
		//int []result = new int[2];
		for (int i = 0; i < num.length; i++) {
			myMap.put( num[i],i);
			}
		for (int i = 0; i < num.length; i++) {
			int v =  myMap.get( target - num[i]);
				if (v != 0 && v > i) {
					return new int[]{i,v};
				}
		}
		return null;
		
		
	}
	public static void main(String[] args) {
		int num[] = new int[]{2,7,11,15};
		Scanner scanner = new Scanner(System.in);
		int target = scanner.nextInt();
		int []array = twoSum(num, target);
		System.out.print("[");
		for (int i = 0; i < array.length; i++) {	
			System.out.print(array[i]+" ");	
			//System.out.print("");
		}
		System.out.print("]");		
	}
}