From 5c8175e0bdd83b51f52bab96c1f06827d3210f06 Mon Sep 17 00:00:00 2001
From: Hao Chen <haoel@hotmail.com>
Date: Tue, 5 Feb 2019 14:44:47 +0800
Subject: [PATCH] New Probelm Solution = "Interval List Intersections"

---
 README.md                                     |  1 +
 .../IntervalListIntersections.cpp             | 94 +++++++++++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 algorithms/cpp/intervalListIntersectons/IntervalListIntersections.cpp

diff --git a/README.md b/README.md
index 92e9cfb..e368948 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,7 @@ LeetCode
 |---| ----- | -------- | ---------- |
 |988|[Smallest String Starting From Leaf](https://leetcode.com/problems/smallest-string-starting-from-leaf/) | [C++](./algorithms/cpp/smallestStringStartingFromLeaf/SmallestStringStartingFromLeaf.cpp)|Medium|
 |987|[Vertical Order Traversal of a Binary Tree](https://leetcode.com/problems/vertical-order-traversal-of-a-binary-tree/) | [C++](./algorithms/cpp/verticalOrderTraversalOfABinaryTree/VerticalOrderTraversalOfABinaryTree.cpp)|Medium|
+|986|[Interval List Intersections](https://leetcode.com/problems/interval-list-intersections/) | [C++](./algorithms/cpp/intervalListIntersectons/IntervalListIntersections.cpp)|Medium|
 |985|[Sum of Even Numbers After Queries](https://leetcode.com/problems/sum-of-even-numbers-after-queries/) | [C++](./algorithms/cpp/sumOfEvenNumbersAfterQueries/SumOfEvenNumbersAfterQueries.cpp)|Easy|
 |984|[String Without AAA or BBB](https://leetcode.com/problems/string-without-aaa-or-bbb/) | [C++](./algorithms/cpp/stringWithoutAAAOrBBB/StringWithoutAAAOrBBB.cpp)|Easy|
 |983|[Minimum Cost For Tickets](https://leetcode.com/problems/minimum-cost-for-tickets/) | [C++](./algorithms/cpp/minimumCostForTickets/MinimumCostForTickets.cpp)|Medium|
diff --git a/algorithms/cpp/intervalListIntersectons/IntervalListIntersections.cpp b/algorithms/cpp/intervalListIntersectons/IntervalListIntersections.cpp
new file mode 100644
index 0000000..8a3112b
--- /dev/null
+++ b/algorithms/cpp/intervalListIntersectons/IntervalListIntersections.cpp
@@ -0,0 +1,94 @@
+// Source : https://leetcode.com/problems/interval-list-intersections/
+// Author : Hao Chen
+// Date   : 2019-02-05
+
+/***************************************************************************************************** 
+ *
+ * Given two lists of closed intervals, each list of intervals is pairwise disjoint and in sorted 
+ * order.
+ * 
+ * Return the intersection of these two interval lists.
+ * 
+ * (Formally, a closed interval [a, b] (with a <= b) denotes the set of real numbers x with a <= x <= 
+ * b.  The intersection of two closed intervals is a set of real numbers that is either empty, or can 
+ * be represented as a closed interval.  For example, the intersection of [1, 3] and [2, 4] is [2, 3].)
+ * 
+ * Example 1:
+ *    
+ *             0   2     5      10     13           23 24 25
+ *      A     +---+     +-------+     +-------------+  +--+
+ *    
+ *               1      5    8     12      15        24 25  26
+ *      B        +------+    +------+      +----------+  +--+
+ *    
+ *              1  2    5    8  10         15      23 24 25
+ *    Ans        ++     +    +--+          +--------+ +  +
+ *    
+ * 
+ * Input: A = [[0,2],[5,10],[13,23],[24,25]], B = [[1,5],[8,12],[15,24],[25,26]]
+ * Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]
+ * Reminder: The inputs and the desired output are lists of Interval objects, and not arrays or lists.
+ * 
+ * Note:
+ * 
+ * 	0 <= A.length < 1000
+ * 	0 <= B.length < 1000
+ * 	0 <= A[i].start, A[i].end, B[i].start, B[i].end < 109
+ * 
+ ******************************************************************************************************/
+
+/**
+ * Definition for an interval.
+ * struct Interval {
+ *     int start;
+ *     int end;
+ *     Interval() : start(0), end(0) {}
+ *     Interval(int s, int e) : start(s), end(e) {}
+ * };
+ */
+class Solution {
+public:
+    //return true if lhs starts earlier than  rhs
+    bool compareInterval(Interval& lhs, Interval& rhs) {
+        return lhs.start < rhs.start;
+    }
+    //check two interval overlapped or not
+    bool overlapped(Interval& lhs, Interval& rhs) {
+        return (compareInterval(lhs, rhs)) ?
+                             lhs.end >= rhs.start:
+                             rhs.end >= lhs.start;
+
+    }
+    //merge two interval - return the intersections of two intervals
+    Interval mergeTwoInterval(Interval& lhs, Interval& rhs) {
+        Interval result;
+        result.start = max(lhs.start, rhs.start);
+        result.end = min(lhs.end, rhs.end);
+        return result;
+    }
+
+    vector<Interval> intervalIntersection(vector<Interval>& A, vector<Interval>& B) {
+        int lenA = A.size();
+        int lenB = B.size();
+
+        vector<Interval> result;
+        if (lenA <=0 || lenB<=0) return result; //edge case
+
+        int i=0, j=0;
+        while ( i < lenA && j < lenB ) {
+            if( overlapped(A[i], B[j]) ) {
+                result.push_back(mergeTwoInterval(A[i], B[j]));
+                // if the current interval is not overlapped with next one,
+                // then we move the next interval.
+                int nexti = i;
+                if ( j==lenB-1 || !overlapped(A[i], B[j+1]) ) nexti=i+1;
+                if ( i==lenA-1 || !overlapped(A[i+1], B[j]) ) j++;
+                i = nexti;
+            }else{
+                //if not overlapped, we just move the next one
+                compareInterval(A[i], B[j]) ? i++ : j++;
+            }
+        }
+        return result;
+    }
+};