[Easy]Two Sum

Two Sum

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

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,

return [0, 1].

Solution

public class Solution {
public int[] twoSum(int[] nums, int target) {
int result[] = new int[2];
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
int index = 0;
for (int num:nums) {
if (map.containsKey(target - num)) {
result[1] = index;
result[0] = map.get(target - num);
return result;
}
map.put(num, index++);
}
return result;
}

}

Analysis

将求和问题转化为查找问题，查找target-num是否存在