two sum solution

Author: jinvicky

two-sum/jinvicky.java

@@ -0,0 +1,35 @@
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ 본래 brute force로 이중 for문으로 풀었다가 map으로 최적화.
+ */
+class Solution {
+    /**
+     * brute force 풀이
+     */
+//    public int[] twoSumByBruteForce(int[] nums, int target) {
+//        for (int i = 0; i < nums.length; i++) {
+//            for (int j = i+1; j < nums.length; j++) {
+//                if (nums[i] + nums[j] == target) {
+//                    return new int[] { i, j };
+//                }
+//            }
+//        }
+//        return new int[2];
+//    }
+
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> numberMap = new HashMap<>();
+        for (int i = 0; i < nums.length; i++) {
+            int required = target - nums[i];
+            Integer index = numberMap.get(required);
+
+            if (index != null) {
+                return new int[] { index, i };
+            }
+            numberMap.put(nums[i], i);
+        }
+        return new int[2];
+    }
+}