每日刷题

70works/day2_plusOne.cpp

+/**
+ * 一次哈希遍历
+ * 解题思路:数值作为map的键，下标作为map的值;
+ * 每次遍历时，如果target-nums[i]在map中能找到值，
+ * 说明target的两个数已经找到,就返回
+*/
+#include <iostream>
+#include<vector>
+#include<map>
+using namespace std;
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        vector<int>res;
+        map<int, int> hashmap;
+        for(int i=0; i< nums.size();i++) {
+            if(hashmap[target-nums[i]] && hashmap[target-nums[i]] != i+1) {
+                res.push_back(i);
+                res.push_back(hashmap[target-nums[i]]-1);
+                return res;
+            }
+
+            //不让hash的下标为负
+            hashmap[nums[i]] = i+1;
+        }
+        return res;
+    }
+};
+int main() {
+    Solution s;
+    vector<int> test= {-2,11, 4, 15, 7,5};
+   
+    for(int i =0; i< s.twoSum(test, 9).size();i++) {
+        cout<< s.twoSum(test, 9)[i]<<endl;
+    }
+    return 0;
+}
\ No newline at end of file

70works/day3_twoSum.js

+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+var twoSum = function(nums, target) {
+    let hashMap = {};
+    for(let i=0; i < nums.length;i++) {
+        let  n = target -nums[i];
+        let find = hashMap[n];
+        if (find!= undefined) return hashMap[find,i];
+        else hashMap[nums[i]] = i;
+    }
+};
+let nums = [2,7,11,15];
+let target = 9;
+twoSum(nums, target);

70works/day4_ Swap Nodes in Pairs.cpp

+#include<iostream>
+using namespace std;
+ struct ListNode {
+      int val;
+      ListNode *next;
+      ListNode(int x) : val(x), next(NULL) {}
+ };
+class Solution {
+public:
+  ListNode* swapPairs(ListNode* head) {
+       if (head == nullptr || head->next == nullptr) return head;
+        ListNode* next = NULL;
+        // 错误原因:递归不需要什么循环，因为递归本身就是循环
+        // while(head!= NULL && head->next != NULL) {
+        next= head->next;
+        head->next = swapPairs(next->next);
+        next->next = head;
+        // }
+        return next;
+    }
+};
+int main() {
+    ListNode* head = new ListNode(1);
+    ListNode* head1 = new ListNode(2);
+    ListNode* head2 = new ListNode(3);
+    ListNode* head3 = new ListNode(4);
+    head->next =head1;
+    head1->next =head2;
+    head2->next =head3;
+    Solution s;
+    s.swapPairs(head);
+    return 0;
+}