Target Sum Problem

Author: pikumar-quotient

LeetCode/Arrays/TargetSum.java

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+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * @author : Piyush Kumar ( spdpiyush )
+ * <p>
+ *     Question Link : https://leetcode.com/problems/two-sum/
+ * </p>
+ */
+public class TargetSum {
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        int[] result = solution.twoSumOptimalApproach(new int[] {3, 2, 4}, 6);
+        for (int value: result) {
+            System.out.println(value);
+        }
+    }
+}
+
+/**
+ * <p>
+ *     Brute Force Approach.
+ *     Time Complexity : O(n * (n-1)) ~ O(n^2)
+ *     Space Complexity : O(1)
+ * </p>
+ */
+class Solution {
+    /**
+     * <p>
+     *     Brute Force Approach.
+     *     Time Complexity : O(n * (n-1)) ~ O(n^2)
+     *     Space Complexity : O(1)
+     * </p>
+     */
+    public int[] twoSum(int[] nums, int target) {
+        for (int i = 0; i < nums.length - 1; i++) {
+            for (int j = i+1; j < nums.length ; j++) {
+                if ((nums[i] + nums[j]) == target) {
+                    return new int[] {i , j};
+                }
+            }
+        }
+        throw new IllegalArgumentException("Target not matched");
+    }
+
+    /**
+     *  Time Complexity : O(n)
+     * @param nums
+     * @param target
+     * @return int[]
+     */
+    public int[] twoSumOptimalApproach(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i =0 ; i < nums.length ; i++) {
+            map.put(nums[i], i);
+        }
+        for (int i = 0; i < nums.length; i++) {
+            int diff = target - nums[i];
+            if (map.containsKey(diff) && map.get(diff) != i) {
+                return new int[] {i, map.get(diff)};
+            }
+        }
+        throw new IllegalArgumentException("Target Not Matched");
+    }
+}
+
+