Question Link

https://leetcode.com/problems/two-sum/

Question Description

Find two value in array that sum up to be target. There is only one solution.
Input: nums = [2,7,11,15], target = 9
Output: [0,1]

Simulation

Solution 1: HashMap with Two Times Array Traversing

Solution 2: HashMap with One Times Array Traversing

Implementation

Solution 1

public int[] twoSum(int[] nums, int target) {
    HashMap < Integer, Integer > map = new HashMap < > ();
    int[] result = new int[2];
    for (int i = 0; i < nums.length; i++) {
        map.put(target - nums[i], i);
    }
    for (int j = 0; j < nums.length; j++) {
        if (map.containsKey(nums[j]) && map.get(nums[j]) != j) {
            result[0] = map.get(nums[j]);
            result[1] = j;
        }
    }
    return result;
}

Solution 2

public int[] twoSum(int[] numbers, int target) {
    int[] result = new int[2];
    Map<Integer, Integer> map = new HashMap<Integer, Integer>();
    for (int i = 0; i < numbers.length; i++) {
        if (map.containsKey(target - numbers[i])) {
            result[1] = i;
            result[0] = map.get(target - numbers[i]);
            return result;
        }
        map.put(numbers[i], i);
    }
    return result;
}