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import java.util.HashMap;
import static util.Asserts.assertEquals;
/**
* 给定一个整数数组 nums 和一个目标值 target，请你在该数组中找出和为目标值的那 两个 整数，并返回他们的数组下标。
*
* 你可以假设每种输入只会对应一个答案。但是，你不能重复利用这个数组中同样的元素。
*
* 示例:
*
* 给定 nums = [2, 7, 11, 15], target = 9
*
* 因为 nums[0] + nums[1] = 2 + 7 = 9
* 所以返回 [0, 1]
*
* 来源：力扣（LeetCode）
* 链接：https://leetcode-cn.com/problems/two-sum
* 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
*
* @author abomb4 2020-01-12
*/
public class Solution1 {
public int[] twoSum(int[] nums, int target) {
final HashMap<Integer, Integer> map = new HashMap<>(nums.length);
for (int i = 0; i < nums.length; i++) {
final int num = nums[i];
final int need = target - num;
final Integer oldIndex = map.get(need);
if (oldIndex != null) {
return new int[]{oldIndex, i};
}
map.put(num, i);
}
throw new IllegalArgumentException("Not found");
}
public static void main(String[] args) {
final Solution1 s = new Solution1();
final int[] result = s.twoSum(new int[]{2, 7, 11, 15}, 9);
assertEquals(2, result.length, "result.length");
assertEquals(0, result[0], "result[0]");
assertEquals(1, result[1], "result[1]");
}
}