string substring 2 pointer problems

Author: piyushkhemka

172. Factorial Trailing Zeroes.cpp

@@ -0,0 +1,13 @@
+class Solution {
+public:
+    int trailingZeroes(int n) {
+        long five = 5;
+        long ans = 0;
+        while(five <= n) {
+            ans += n/five;
+            five = five * 5;
+        }
+        return ans;
+
+    }
+};

24. Swap Nodes in Pairs.cpp

@@ -0,0 +1,37 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* swapPairs(ListNode* head) {
+
+        if(!head)
+            return nullptr;
+
+        if(!(head->next))
+            return head;
+
+        ListNode *newhead = head->next;
+        ListNode *cur = head;
+        ListNode *next;
+        ListNode *prev = nullptr;
+
+        while(cur && cur->next) {
+            next = cur->next;
+            cur->next = next->next;
+            next->next = cur;
+
+            if (prev) {
+                prev->next = next;
+            }
+            prev = cur;
+            cur = cur->next;
+        }
+        return newhead;
+    }
+};

Search a 2d array.cpp 74. Search a 2d matrix.cpp

@@ -0,0 +1,50 @@
+class Solution {
+public:
+    string minWindow(string s, string t) {
+
+        if(s.empty() || t.empty())
+            return "";
+            
+        unordered_map<char, int> m;
+
+        for(auto c:t) {
+            m[c]++;
+        }
+
+        int n = s.length();
+        int end = 0;
+        int start = 0;
+        int minlen = INT_MAX;
+        int counter = t.length();
+        string result = "";
+
+        while(end < n) {
+
+            if(m[s[end]] > 0)
+                counter--;
+
+            m[s[end]]--;
+
+            end++;
+
+            while (counter == 0) {
+
+                if (end - start < minlen) {
+                    minlen = end-start;
+                    result = s.substr(start, minlen);
+                }
+                m[s[start]]++;
+
+                if(m[s[start]] > 0)
+                    counter++;
+
+                start++;
+            }
+
+        }
+
+        return result;
+
+
+    }
+};