[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.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

vector<int> lcs(vector<int>& a, vector<int>& b) {
    int n = a.size(), m = b.size();
    vector<vector<int> > dp(n + 1, vector<int> (m + 1, 0));
    for (int i = 1 ;i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (a[i - 1] == b[j - 1]) dp[i][j] = dp[i - 1][j - 1] + 1;
            else dp[i][j] = max(dp[i][j - 1], dp[i - 1][j]);
        }
    }
    vector<int> res;
    for (int i = n, j = m; i >= 1 && j >= 1;) {
        if (a[i - 1] == b[j - 1]) {
            res.push_back(a[i - 1]);
            i--;
            j--;
        }
        else if (dp[i - 1][j] >= dp[i][j - 1]) i--;
        else j--;
    }
    reverse(res.begin(), res.end());
    return res;
}

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int n, m;
    while (scanf("%d %d", &n, &m) != EOF) {
        vector<int> a(n);
        vector<int> b(m);
        for (int i = 0; i < n; i++)
            scanf("%d", &a[i]);
        for (int i = 0; i < m; i++)
            scanf("%d", &b[i]);
        vector<int> res = lcs(a, b);
        for (int i = 0; i < (int)res.size(); i++)
            printf("%d ", res[i]);
        printf("
");
    }
    return 0;
}

 Well, try this problem here and get Accepted :)