Two Sum

Author: forest000014

two-sum/forest000014.java

@@ -0,0 +1,64 @@
+/*
+runtime 23 ms, beats 50.28%
+memory 45.12 MB, beats 20.14%
+
+time complexity: O(nlogn)
+- numsArray 정렬: O(nlogn)
+- binary search: O(nlogn)
+  - i iteration: O(n)
+  - i번째 binary search: O(logn)
+
+space complexity: O(n)
+- numsArray: O(n)
+*/
+
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        ArrayList<Tuple> numsArray = IntStream.range(0, nums.length)
+                .mapToObj(i -> new Tuple(i, nums[i]))
+                .collect(Collectors.toCollection(ArrayList::new));
+
+        numsArray.sort(Comparator.comparing(tuple -> tuple.val));
+
+        int n = numsArray.size();
+
+        for (int i = 0; i < n; i++) {
+            int x = target - numsArray.get(i).val;
+            int j = -1;
+            int l = i + 1;
+            int r = n - 1;
+            boolean found = false;
+            while (l <= r) {
+                int m = (r - l) / 2 + l;
+                if (numsArray.get(m).val == x) {
+                    j = m;
+                    found = true;
+                    break;
+                } else if (numsArray.get(m).val < x) {
+                    l = m + 1;
+                } else {
+                    r = m - 1;
+                }
+            }
+
+            if (found) {
+                int[] ans = new int[2];
+                ans[0] = numsArray.get(i).ref;
+                ans[1] = numsArray.get(j).ref;
+                return ans;
+            }
+        }
+
+        return null;
+    }
+
+    public class Tuple {
+        public final Integer ref;
+        public final Integer val;
+
+        public Tuple(Integer ref, Integer val) {
+            this.ref = ref;
+            this.val = val;
+        }
+    }
+}