[LEET-532] add 532

fishercoder1534 · fishercoder1534 · commit ce0feba214e7 · 2017-03-05T16:22:01.000-08:00
diff --git a/leetcode-algorithms/README.md b/leetcode-algorithms/README.md
@@ -4,6 +4,7 @@
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
 |535|[Encode and Decode TinyURL](https://leetcode.com/problems/encode-and-decode-tinyurl/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/EncodeandDecodeTinyURL.java) | O(1) |O(n) | Medium | Design
+|532|[K-diff Pairs in an Array](https://leetcode.com/problems/k-diff-pairs-in-an-array/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/KdiffPairsinanArray.java) | O(n) |O(n) | Easy | HashMap
 |531|[Lonely Pixel I](https://leetcode.com/problems/lonely-pixel-i/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/LonelyPixelI.java) | O(m*n) |O(1) | Medium | 
 |530|[Minimum Absolute Difference in BST](https://leetcode.com/problems/minimum-absolute-difference-in-bst/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/MinimumAbsoluteDifferenceinBST.java) | O(n) |O(n) | Easy| DFS
 |529|[Minesweeper](https://leetcode.com/problems/minesweeper/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/Minesweeper.java) | O(m*n) |O(k) | Medium | BFS
diff --git a/leetcode-algorithms/src/main/java/com/stevesun/solutions/KdiffPairsinanArray.java b/leetcode-algorithms/src/main/java/com/stevesun/solutions/KdiffPairsinanArray.java
@@ -0,0 +1,63 @@
+package com.stevesun.solutions;
+
+import java.util.*;
+
+/**
+ * Given an array of integers and an integer k, you need to find the number of unique k-diff pairs in the array. Here a k-diff pair is defined as an integer pair (i, j), where i and j are both numbers in the array and their absolute difference is k.
+
+ Example 1:
+ Input: [3, 1, 4, 1, 5], k = 2
+ Output: 2
+ Explanation: There are two 2-diff pairs in the array, (1, 3) and (3, 5).
+ Although we have two 1s in the input, we should only return the number of unique pairs.
+
+ Example 2:
+ Input:[1, 2, 3, 4, 5], k = 1
+ Output: 4
+ Explanation: There are four 1-diff pairs in the array, (1, 2), (2, 3), (3, 4) and (4, 5).
+
+ Example 3:
+ Input: [1, 3, 1, 5, 4], k = 0
+ Output: 1
+ Explanation: There is one 0-diff pair in the array, (1, 1).
+
+ Note:
+ The pairs (i, j) and (j, i) count as the same pair.
+ The length of the array won't exceed 10,000.
+ All the integers in the given input belong to the range: [-1e7, 1e7].
+ */
+public class KdiffPairsinanArray {
+
+    //this O(n^2) will result in TLE
+    public int findPairs_On2(int[] nums, int k) {
+        Set<List<Integer>> pairsSet = new HashSet<>();
+        for (int i = 0; i < nums.length-1; i++) {
+            for (int j = i+1; j < nums.length; j++) {
+                if (Math.abs(nums[j] - nums[i]) == k) {
+                    pairsSet.add(nums[i] > nums[j] ? Arrays.asList(nums[j], nums[i]) : Arrays.asList(nums[i], nums[j]));
+                }
+            }
+        }
+        return pairsSet.size();
+    }
+
+    public int findPairs(int[] nums, int k) {
+        if (nums == null || nums.length == 0 || k < 0) return 0;
+
+        Map<Integer, Integer> map = new HashMap();
+        for (int i : nums) {
+            map.put(i, map.getOrDefault(i, 0) + 1);
+        }
+
+        int answer = 0;
+        for (int key : map.keySet()) {
+            if (k == 0) {
+                if (map.get(key) >= 2) answer++;
+            } else {
+                if (map.containsKey(key + k)) answer++;
+            }
+        }
+        return answer;
+    }
+
+}
diff --git a/leetcode-algorithms/src/test/java/com/stevesun/KdiffPairsinanArrayTest.java b/leetcode-algorithms/src/test/java/com/stevesun/KdiffPairsinanArrayTest.java
