#### Two Sum Problem

A
a
```package com.thealgorithms.misc;

import java.util.*;
import java.util.stream.Collectors;

public class TwoSumProblem {

public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
System.out.print("Enter the target sum ");
int ts = scan.nextInt();
System.out.print("Enter the number of elements in the array ");
int n = scan.nextInt();
int arr[] = new int[n];
for (int i = 0; i < n; i++) {
arr[i] = scan.nextInt();
}
TwoSumProblem t = new TwoSumProblem();
System.out.println(
"Brute Force Approach\n" +
Arrays.toString(t.BruteForce(arr, ts)) +
"\n"
);
System.out.println(
"Two Pointer Approach\n" +
Arrays.toString(t.TwoPointer(arr, ts)) +
"\n"
);
System.out.println(
"Hashmap Approach\n" + Arrays.toString(t.HashMap(arr, ts))
);
}

public int[] BruteForce(int[] nums, int target) {
//Brute Force Approach
int ans[] = new int[2];
for (int i = 0; i < nums.length; i++) {
for (int j = i + 1; j < nums.length; j++) {
if (nums[i] + nums[j] == target) {
ans[0] = i;
ans[1] = j;

break;
}
}
}

return ans;
}

public int[] TwoPointer(int[] nums, int target) {
// HashMap Approach
int ans[] = new int[2];
HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>();
for (int i = 0; i < nums.length; i++) {
hm.put(i, nums[i]);
}
HashMap<Integer, Integer> temp = hm
.entrySet()
.stream()
.sorted((i1, i2) -> i1.getValue().compareTo(i2.getValue()))
.collect(
Collectors.toMap(
Map.Entry::getKey,
Map.Entry::getValue,
(e1, e2) -> e1,
)
);

int start = 0;
int end = nums.length - 1;
while (start < end) {
int currSum = (Integer) temp.values().toArray()[start] +
(Integer) temp.values().toArray()[end];

if (currSum == target) {
ans[0] = (Integer) temp.keySet().toArray()[start];
ans[1] = (Integer) temp.keySet().toArray()[end];
break;
} else if (currSum > target) {
end -= 1;
} else if (currSum < target) {
start += 1;
}
}
return ans;
}

public int[] HashMap(int[] nums, int target) {
//Using Hashmaps
int ans[] = new int[2];
HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>();
for (int i = 0; i < nums.length; i++) {
hm.put(nums[i], i);
}
for (int i = 0; i < nums.length; i++) {
int t = target - nums[i];
if (hm.containsKey(t) && hm.get(t) != i) {
ans[0] = i;
ans[1] = hm.get(t);
break;
}
}

return ans;
}
}
```