Solution.java

importjava.util.*;

classSolution {
publicint[] twoSum(int[] nums, inttarget) {
HashMap<Integer, Integer> dict = newHashMap<Integer, Integer>(); /* HashMap只能装integer，不能装int */
int[] result = newint[2];
for (inti = 0; i < nums.length; i++)
 {
dict.put(nums[i], i); // 顺序的map映射: value->index
 }
for (inti = 0; i < nums.length; i++)
 {
intquery = target - nums[i];
if (dict.containsKey(query) && dict.get(query) > i) // dict[query] > i是为了防止重复计算
 {
result[0] = i;
result[1] = dict.get(query);
break;
 }
 }
returnresult;
 }

// Test
publicstaticvoidmain(String[] args) {
Solutionsol = newSolution();
int[] nums = {2,7,11,15};
inttarget = 9;
int[] res = sol.twoSum(nums, target);
System.out.println(Arrays.toString(res));
 }
}