LeetCode: Longest Consecutive Sequence

想到map了，可惜没想到用erase来节省空间，看了网上答案

 1 class Solution {

 2 public:

 3     int longestConsecutive(vector<int> &num) {

 4         // Start typing your C/C++ solution below

 5         // DO NOT write int main() function

 6         map<int, int> rec;

 7         for (int i = 0; i < num.size(); i++) rec.insert(pair<int, int>(num[i], 1));

 8         int maxcon = 0;

 9         for (int i = 0; i < num.size(); i++) {

10             map<int, int>::iterator it = rec.find(num[i]);

11             if (it != rec.end()) {

12                 int left = num[i]-1;

13                 int right = num[i]+1;

14                 while (1) {

15                     map<int, int>::iterator iter = rec.find(left);

16                     if (iter != rec.end()) {

17                         left--;

18                         rec.erase(iter);

19                     }

20                     else break;

21                 }

22                 left++;

23                 while (1) {

24                     map<int, int>::iterator iter = rec.find(right);

25                     if (iter != rec. end()) {

26                         right++;

27                         rec.erase(iter);

28                     }

29                     else break;

30                 }

31                 right--;

32                 maxcon = max(maxcon, right - left + 1);

33                 rec.erase(it);

34             }

35         }

36         return maxcon;

37     }

38 };

 贴上自己写的更加简单的代码

 1 class Solution {

 2 public:

 3     int longestConsecutive(vector<int> &num) {

 4         // Start typing your C/C++ solution below

 5         // DO NOT write int main() function

 6         map<int, int> S;

 7         int sum = 0;

 8         for (int i = 0; i < num.size(); i++) S[num[i]] = 1;

 9         for (int i = 0; i < num.size(); i++) {

10             if (S.count(num[i])) {

11                 int left = 1;

12                 int tmp = num[i];

13                 while (S.count(tmp-left)) {

14                     S.erase(tmp-left);

15                     left++;

16                 }

17                 int right = 1;

18                 while (S.count(tmp+right)) {

19                     S.erase(tmp+right);

20                     right++;

21                 }

22                 S.erase(tmp);

23                 sum = max(sum, left+right-1);

24             }

25         }

26         return sum;

27     }

28 };

 C#

 1 public class Solution {

 2     public int LongestConsecutive(int[] nums) {

 3         Dictionary<int, int> S = new Dictionary<int, int>();

 4         int ans = 0;

 5         for (int i = 0; i < nums.Length; i++) {

 6             if (!S.ContainsKey(nums[i])) S.Add(nums[i], 1);

 7         }

 8         for (int i = 0; i < nums.Length; i++) {

 9             if (S.ContainsKey(nums[i])) {

10                 int left = 1;

11                 int tmp = nums[i];

12                 while (S.ContainsKey(tmp - left)) {

13                     S.Remove(tmp - left);

14                     left++;

15                 }

16                 int right = 1;

17                 while (S.ContainsKey(tmp + right)) {

18                     S.Remove(tmp + right);

19                     right++;

20                 }

21                 S.Remove(tmp);

22                 ans = Math.Max(ans, left + right - 1);

23             }

24         }

25         return ans;

26     }

27 }

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