HackerRank# The Longest Common Subsequence
LCD，经典动归，O(n^2)复杂度
因为要输出子序列，所以啰嗦一些
1 #include <cmath> 2 #include <cstdio> 3 #include <vector> 4 #include <iostream> 5 #include <algorithm> 6 #include <cstring> 7 using namespace std; 8 9 #define MAX_LEN 128 10 11 int n, m; 12 int a[MAX_LEN], b[MAX_LEN]; 13 int lcd[MAX_LEN][MAX_LEN]; 14 int start_index_a[MAX_LEN][MAX_LEN]; 15 int start_index_b[MAX_LEN][MAX_LEN]; 16 17 int main() { 18 /* Enter your code here. Read input from STDIN. Print output to STDOUT */ 19 cin >> n >> m; 20 for (int i = 0; i < n; i++) 21 cin >> a[i]; 22 for (int i = 0; i < m; i++) 23 cin >> b[i]; 24 memset(lcd, 0, sizeof(lcd)); 25 memset(start_index_a, 0, sizeof(start_index_a)); 26 for (int j = 0; j < m; j++) 27 start_index_a[n][j] = start_index_b[n][j] = -1; 28 for (int i = 0; i < n; i++) 29 start_index_a[i][m] = start_index_b[i][m] = -1; 30 for (int i = n - 1; i >= 0; i--) { 31 for (int j = m - 1; j >= 0; j--) { 32 if (a[i] == b[j]) { 33 lcd[i][j] = lcd[i + 1][j + 1] + 1; 34 start_index_a[i][j] = i; 35 start_index_b[i][j] = j; 36 } else if (lcd[i + 1][j] > lcd[i][j + 1]) { 37 lcd[i][j] = lcd[i + 1][j]; 38 start_index_a[i][j] = start_index_a[i + 1][j]; 39 start_index_b[i][j] = start_index_b[i + 1][j]; 40 } else { 41 lcd[i][j] = lcd[i][j + 1]; 42 start_index_a[i][j] = start_index_a[i][j + 1]; 43 start_index_b[i][j] = start_index_b[i][j + 1]; 44 } 45 } 46 } 47 48 int i = start_index_a[0][0]; 49 int j = start_index_b[0][0]; 50 while (i >= 0 && j >= 0) { 51 cout << a[i] << " "; 52 int ii = start_index_a[i + 1][j + 1]; 53 int jj = start_index_b[i + 1][j + 1]; 54 i = ii; 55 j = jj; 56 } 57 cout << endl; 58 return 0; 59 }
