import java.util.HashMap;

class Solution {

public int[] twoSum(int[] nums, int target) {

// Approach : using HashMap to get index with the element in O(n) time

// complexity

// SpaceComplexity is also O(n)

HashMap<Integer, Integer> numIndexMap = new HashMap<Integer, Integer>();

// Make key and value HashMap

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

int num = nums[i];

numIndexMap.put(num, i);

}

// Search for the other operand looping nums

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

int num = nums[i];

int operand = target - num;

Integer index = numIndexMap.get(operand);

boolean indexExists = index != null;

boolean indexExistsAndIndexIsNotTheNum = indexExists && i != index;

if (indexExistsAndIndexIsNotTheNum) {

return new int[] { i, index };

}

}

// If the valid answer is always exists this is not needed

// But the compiler don't know about that

return new int[2];

}

}