https://leetcode.com/problems/3sum/description/

interview_prep/algorithm/java/ide_handicapped/3sum/Solution.java

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+import java.util.AbstractList;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+class Solution {
+    private List<List<Integer>> res;
+
+    public List<List<Integer>> threeSum(int[] nums) {
+
+        return new AbstractList<List<Integer>>() {
+            public List<Integer> get(int index) {
+                init();
+                return res.get(index);
+            }
+
+            public int size() {
+                init();
+                return res.size();
+            }
+
+            private void init() {
+                if (res != null)
+                    return;
+                Arrays.sort(nums);
+                int l, r, sum;
+                final Set<List<Integer>> tempRes = new HashSet<>();
+                for (int i = 0; i < nums.length - 2; ++i) {
+                    l = i + 1;
+                    r = nums.length - 1;
+                    while (l < r) {
+                        sum = nums[i] + nums[l] + nums[r];
+                        if (sum == 0)
+                            tempRes.add(Arrays.asList(nums[i], nums[l], nums[r]));
+                        if (sum < 0)
+                            ++l;
+                        else
+                            --r;
+                    }
+                }
+                res = new ArrayList<List<Integer>>(tempRes);
+            }
+
+        };
+    }
+
+    public static void main(String[] args) {
+        // https://leetcode.com/problems/3sum/description/
+        t1();
+        t2();
+        t3();
+
+    }
+
+    public static void t1() {
+        final Solution sol = new Solution();
+        final List res = sol.threeSum(new int[] { -1, 0, 1, 2, -1, -4 });
+        assert res.contains(Stream.of(-1, -1, 2).collect(Collectors.toList()));
+        assert res.contains(Stream.of(-1, 0, 1).collect(Collectors.toList()));
+        // System.out.println(res);
+    }
+
+    public static void t2() {
+        final Solution sol = new Solution();
+        final List res = sol.threeSum(new int[] { 0, 1, 1 });
+        assert res.isEmpty();
+    }
+
+    public static void t3() {
+        final Solution sol = new Solution();
+        final List res = sol.threeSum(new int[] { 0, 0, 0 });
+        assert res.contains(Stream.of(0, 0, 0).collect(Collectors.toList()));
+        // System.out.println(res);
+    }
+
+    public List<List<Integer>> threeSumSlow(int[] nums) {
+        if (nums == null || nums.length == 0)
+            return Collections.emptyList();
+        Arrays.sort(nums);
+        int l, r, sum;
+        final Set<List<Integer>> tempRes = new HashSet<>();
+        for (int i = 0; i < nums.length - 2; ++i) {
+            l = i + 1;
+            r = nums.length - 1;
+            while (l < r) {
+                sum = nums[i] + nums[l] + nums[r];
+                if (sum == 0)
+                    tempRes.add(Arrays.asList(nums[i], nums[l], nums[r]));
+                if (sum < 0)
+                    ++l;
+                else
+                    --r;
+            }
+        }
+        return new ArrayList<List<Integer>>(tempRes);
+    }
+}