package leetcode;import java.util.HashMap;import java.util.Map;/** * @author mercy *Example: *Given nums = [2, 7, 11, 15], target = 9, *Because nums[0] + nums[1] = 2 + 7 = 9, *return [0, 1]. */public class TwoSum {	public static void main(String[] args) {		int[] nums={2,0,4,9,5,7,10,9};		int target=12;		int[] arr=twoSum1(nums,target);		System.out.println(arr[0]+"--"+arr[1]);	}	public static 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 other=target-nums[i];			if(map.containsKey(other)&&map.get(other)!=i){				 return new int[] { i, map.get(other) };			}		}		throw new IllegalArgumentException("No two sum solution");    }	/**	 * @param nums	 * @param target	 * @return	 * 用Map方法	 * @author mercy	 */	public static int[] twoSum1(int[] nums, int target) {		Map<Integer,Integer> map=new HashMap<>();		for(int i=0;i<nums.length;i++){			int other=target-nums[i];			if(map.containsKey(other)){				return new int[]{map.get(other),i};			}			map.put(nums[i], i);		}			throw new IllegalArgumentException("No two sum solution");    }		/**	 * @param nums	 * @param target	 * @return	 * 传统的方法	 * @author mercy	 */	public static int[] twoSum2(int[] nums, int target) {		for(int i=0;i<nums.length;i++){			for(int j=i+1;j<nums.length;j++){				if(nums[j]==target-nums[i]){					return new int[] {i,j};				}			}		}		throw new IllegalArgumentException("No two sum solution");    }}

1：TwoSum(如果两个和为某个数，找出这俩数的位置)