2020/01/26

Author: wr786

C++/23 Merge k Sorted Lists.cpp

@@ -0,0 +1,48 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) { // 代码复用
+        if(l1 == NULL) return l2;
+        if(l2 == NULL) return l1;
+        if(l2->val < l1->val) swap(l1, l2);
+        ListNode* curl1 = l1;
+        ListNode* lastl1 = l1;
+        while(l2 != NULL) { // merge l2 into l1
+            if(curl1 == NULL) {
+                lastl1->next = l2;
+                break;
+            } else {
+                if(curl1->val <= l2->val) {
+                    lastl1 = curl1;
+                    curl1 = curl1->next;
+                } else {
+                    lastl1->next = l2;
+                    lastl1 = l2;
+                    ListNode* tmp = l2->next;
+                    l2->next = curl1;
+                    l2 = tmp;
+                }
+            }
+        }
+        return l1;
+    }
+    ListNode* mergeKLists(vector<ListNode*>& lists) { // 分治
+        int n = lists.size();
+        int interval = 1;
+        while(interval < n) {
+            for(int i=0; i<n-interval; i+=2*interval) {
+                lists[i] = mergeTwoLists(lists[i], lists[i + interval]);
+            }
+            interval *= 2;
+        }
+        if(n) return lists[0];
+        else return NULL;
+    }
+};

C++/263 Ugly Number.cpp

@@ -0,0 +1,10 @@
+class Solution {
+public:
+    bool isUgly(int num) {
+        if(num <= 0) return false;
+        while(num && num % 2 == 0) num /= 2;
+        while(num && num % 3 == 0) num /= 3;
+        while(num && num % 5 == 0) num /= 5;
+        return (num == 1);
+    }
+};

C++/28 Implement strStr().cpp

@@ -0,0 +1,18 @@
+class Solution {
+public:
+    int strStr(string haystack, string needle) {
+        if(needle == "") return 0;
+        int m = haystack.length(), n = needle.length();
+        int curPos = 0;
+        for(int i=0; i<m; i++) {
+            if(haystack[i] == needle[curPos]) {
+                curPos++;
+                if(curPos == n) return i - curPos + 1;
+            } else {
+                i = i - curPos;
+                curPos = 0;
+            }         
+        }
+        return -1;
+    }
+};