[HackerRank] The Longest Common Subsequence
This is the classic LCS problem. Since it requires you to print one longest common subsequence, just use the O(m*n)-space version here.
My accepted code is as follows.
1 #include <iostream> 2 #include <vector> 3 #include <algorithm> 4 5 using namespace std; 6 7 vector<int> lcs(vector<int>& a, vector<int>& b) { 8 int n = a.size(), m = b.size(); 9 vector<vector<int> > dp(n + 1, vector<int> (m + 1, 0)); 10 for (int i = 1 ;i <= n; i++) { 11 for (int j = 1; j <= m; j++) { 12 if (a[i - 1] == b[j - 1]) dp[i][j] = dp[i - 1][j - 1] + 1; 13 else dp[i][j] = max(dp[i][j - 1], dp[i - 1][j]); 14 } 15 } 16 vector<int> res; 17 for (int i = n, j = m; i >= 1 && j >= 1;) { 18 if (a[i - 1] == b[j - 1]) { 19 res.push_back(a[i - 1]); 20 i--; 21 j--; 22 } 23 else if (dp[i - 1][j] >= dp[i][j - 1]) i--; 24 else j--; 25 } 26 reverse(res.begin(), res.end()); 27 return res; 28 } 29 30 int main() { 31 /* Enter your code here. Read input from STDIN. Print output to STDOUT */ 32 int n, m; 33 while (scanf("%d %d", &n, &m) != EOF) { 34 vector<int> a(n); 35 vector<int> b(m); 36 for (int i = 0; i < n; i++) 37 scanf("%d", &a[i]); 38 for (int i = 0; i < m; i++) 39 scanf("%d", &b[i]); 40 vector<int> res = lcs(a, b); 41 for (int i = 0; i < (int)res.size(); i++) 42 printf("%d ", res[i]); 43 printf("\n"); 44 } 45 return 0; 46 }
Well, try this problem here and get Accepted :)
