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Author: xwk1246

.gitignore

@@ -1,3 +1,3 @@
 *
-!*.*
+!*.cpp
 !*/

1.cpp

@@ -1,17 +1,7 @@
 #include <vector>
 #include <unordered_map>
-#include <unordered_set>
-#include <cmath>
 using namespace std;
 
 vector<int> twoSum(vector<int>& nums, int target) {
-    unordered_map<int, int>record;
-    for (int i = 0; i < nums.size(); i++) {
-        unordered_map<int, int>::iterator result;
-        if ((result = record.find(target - nums[i])) != record.end()) {
-            return { i, result->second };
-        }
-        record.insert(pair<int, int>(nums[i], i));
-    }
-    return {};
+
 }

1.two-sum.cpp

@@ -0,0 +1,36 @@
+/*
+ * @lc app=leetcode id=1 lang=cpp
+ *
+ * [1] Two Sum
+ */
+
+ // @lc code=start
+#include <unordered_map>
+#include <vector>
+using namespace std;
+
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        unordered_map<int, int> record;
+        int index = 0;
+
+        for (int num : nums) {
+            auto tmp = record.find(target - num);
+            if (tmp != record.end()) {
+                return { index , tmp->second };
+            }
+            record.insert(pair<int, int>(num, index));
+            index++;
+        }
+        return {};
+    }
+};
+// @lc code=end
+
+int main() {
+    vector<int> nums = { 3, 2, 4 };
+    int target = 6;
+    Solution S1;
+    S1.twoSum(nums, target);
+}

15.3-sum.cpp

@@ -0,0 +1,50 @@
+/*
+ * @lc app=leetcode id=15 lang=cpp
+ *
+ * [15] 3Sum
+ */
+
+ // @lc code=start
+#include <vector>
+#include <algorithm>
+using namespace std;
+
+class Solution {
+public:
+    vector<vector<int>> threeSum(vector<int>& nums) {
+        sort(nums.begin(), nums.end());
+        vector<vector<int>> result;
+        int right;
+        int left;
+        for (int i = 0; i < nums.size(); i++) {
+            if (i > 0 && nums[i - 1] == nums[i])continue;
+            right = nums.size() - 1;
+            left = i + 1;
+            while (left < right) {
+                if (nums[i] + nums[right] + nums[left] < 0) {
+                    left++;
+                }
+                else if (nums[i] + nums[right] + nums[left] > 0) {
+                    right--;
+                }
+                else {
+                    result.push_back({ nums[i], nums[left], nums[right] });
+                    while (left < right && nums[left] == nums[left + 1])left++;
+                    while (left < right && nums[right - 1] == nums[right])right--;
+                    left++;
+                    right--;
+                }
+            }
+
+        }
+        return result;
+    }
+};
+// @lc code=end
+int main() {
+    Solution s;
+    vector<int> nums = { -1,0,1 };
+    s.threeSum(nums);
+    return 0;
+}
+

151.reverse-words-in-a-string.cpp

@@ -0,0 +1,50 @@
+#include <string>
+#include <iostream>
+#include <algorithm>
+using namespace std;
+
+/*
+ * @lc app=leetcode id=151 lang=cpp
+ *
+ * [151] Reverse Words in a String
+ */
+
+ // @lc code=start
+class Solution {
+public:
+    string reverseWords(string s) {
+        int slow = 0, fast = 0;
+        reverse(s.begin(), s.end());
+        while (fast < s.size()) {
+            if (fast == 0 && s[fast] == ' ' || (s[fast] == ' ' && s[fast - 1] == ' ')) {
+                fast++;
+                continue;
+            }
+            s[slow] = s[fast];
+            slow++;
+            fast++;
+        }
+        s.resize(slow);
+        while (s.back() == ' ') {
+            s.pop_back();
+        }
+        for (slow = 0, fast = 0; fast < (int)s.size(); ) {
+            while (s[fast] != ' ' && fast < s.size()) {
+                fast++;
+            };
+            reverse(s.begin() + slow, s.begin() + fast);
+            fast++;
+            slow = fast;
+        }
+        return s;
+    }
+
+};
+// @lc code=end
+
+int main() {
+    Solution S1;
+    cout << S1.reverseWords(" a ");
+    return 0;
+
+}

18.4-sum.cpp

@@ -0,0 +1,49 @@
+#include <vector>
+#include <iostream>
+#include <algorithm>
+using namespace std;
+/*
+ * @lc app=leetcode id=18 lang=cpp
+ *
+ * [18] 4Sum
+ */
+
+ // -2,-1,0,0,1,2
+  // @lc code=start
+class Solution {
+public:
+    vector<vector<int>> fourSum(vector<int>& nums, int target) {
+        sort(nums.begin(), nums.end());
+        vector<vector<int>>result;
+        for (int i = 0; i < nums.size(); i++) {
+            while (i > 0 && i < nums.size() && nums[i] == nums[i - 1])i++;
+            for (int j = i + 1; j < nums.size(); j++) {
+                while (j > i + 1 && j < nums.size() && nums[j] == nums[j - 1])j++;
+                int left, right;
+                left = j + 1;
+                right = nums.size() - 1;
+                while (left < right) {
+                    long long sum = (long long)nums[i] + (long long)nums[j] + (long long)nums[left] + (long long)nums[right];
+                    if (sum > target)right--;
+                    else if (sum < target)left++;
+                    else {
+                        while (left < right && nums[left] == nums[left + 1])left++;
+                        while (left < right && nums[right] == nums[right - 1])right--;
+                        result.push_back({ nums[i], nums[j], nums[left], nums[right] });
+                        left++;
+                        right--;
+                    }
+                }
+            }
+        }
+        return result;
+
+    }
+};
+// @lc code=end
+int main() {
+    Solution S1;
+    vector<int>tmp = { 1000000000,1000000000,1000000000,1000000000 };
+    S1.fourSum(tmp, 0);
+
+}

28.implement-str-str.cpp

@@ -0,0 +1,17 @@
+#include <string>
+using namespace std;
+/*
+ * @lc app=leetcode id=28 lang=cpp
+ *
+ * [28] Implement strStr()
+ */
+
+ // @lc code=start
+class Solution {
+public:
+    int strStr(string haystack, string needle) {
+
+    }
+};
+// @lc code=end
+

344.reverse-string.cpp

@@ -0,0 +1,27 @@
+#include <vector>
+#include <algorithm>
+using namespace std;
+/*
+ * @lc app=leetcode id=344 lang=cpp
+ *
+ * [344] Reverse String
+ */
+
+ // @lc code=start
+class Solution {
+public:
+    void reverseString(vector<char>& s) {
+        for (int i = 0; i < s.size() / 2;i++) {
+            swap(s[i], s[s.size() - 1 - i]);
+        }
+    }
+
+};
+// @lc code=end
+
+int main() {
+    Solution S1;
+    vector<char>s = { 'h', 'e', 'l', 'l', 'o' };
+    S1.reverseString(s);
+}
+

383.ransom-note.cpp

@@ -0,0 +1,38 @@
+/*
+ * @lc app=leetcode id=383 lang=cpp
+ *
+ * [383] Ransom Note
+ */
+
+ // @lc code=start
+#include <string>
+#include <unordered_map>
+#include <vector>
+#include <iostream>
+
+using namespace std;
+
+
+class Solution {
+public:
+    bool canConstruct(string ransomNote, string magazine) {
+        vector<int>record(26, 0);
+        for (auto a : magazine) {
+            record[a - 'a']++;
+        }
+        for (auto a : ransomNote) {
+            if (record[a - 'a'] <= 0) {
+                return false;
+            }
+            record[a - 'a']--;
+        }
+        return true;
+    }
+};
+// @lc code=end
+
+int main() {
+    Solution s;
+    cout << s.canConstruct("aa", "ab");
+}
+

541.reverse-string-ii.cpp

@@ -0,0 +1,33 @@
+#include <vector>
+#include <string>
+#include <algorithm>
+#include <iostream>
+using namespace std;
+/*
+ * @lc app=leetcode id=541 lang=cpp
+ *
+ * [541] Reverse String II
+ */
+
+ // @lc code=start
+class Solution {
+public:
+    string reverseStr(string s, int k) {
+        for (int i = 0; i < s.length(); i += 2 * k) {
+            if ((s.end() - s.begin() - i) < k) {
+                reverse(s.begin() + i, s.end());
+                continue;
+            }
+            reverse(s.begin() + i, s.begin() + k + i);
+        }
+        return s;
+    }
+};
+// @lc code=end
+int main() {
+    Solution S1;
+    cout << S1.reverseStr("a", 1);
+    return 0;
+
+}
+