import java.util.HashMap;

import java.util.Map;

/**

* 借助map的检索特性减少遍历次数

*/

public class Solution1 {

public static void main(String[] args) {

int []nums = {2, 7, 11, 15};

int target = 9;

int[] ints = twoSum(nums, target);

System.out.println(ints[0]+"--"+ints[1]);

}

private static int[] twoSum(int[] nums, int target) {

Map<Integer,Integer> tracer = new HashMap<>();

for (int i = 0; i < nums.length; i++) {

int num = nums[i];

if(tracer.containsKey(num)){

int value = tracer.get(num);

return new int[]{value,i};

}else{

tracer.put(target-num,i);

}

}

return new int[]{};

}

}