Dp/LCS.h

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• Last update: 2025-10-06 23:30:53+07:00

Depends on

• template.h

Code

#include "../template.h"


// Longest common substring with trace

struct Trace {
    int i, j;
    char c;
    Trace(int _i = 0, int _j = 0, char _c = '\0'): i(_i), j(_j), c(_c) {}
};

void solve() {
    string s1, s2; cin >> s1 >> s2;
    s1 = "#" + s1;
    s2 = "#" + s2;
    int n = s1.size(), m = s2.size();
    int dp[n][m];
    Trace par[n][m] = {};
    memset(dp, 0, sizeof dp);
    for (int i = 1; i < n; i++) {
        for (int j = 1; j < m; j++) {
            if (s1[i] == s2[j]) {
                dp[i][j] = dp[i-1][j-1] + 1;
                par[i][j] = Trace(i-1, j-1, s1[i]);
            } else {
                if (dp[i][j-1] >= dp[i-1][j]) {
                    dp[i][j] = dp[i][j-1];
                    par[i][j] = Trace(i, j-1);
                } else {
                    dp[i][j] = dp[i-1][j];
                    par[i][j] = Trace(i-1, j);
                }
            }
        }
    }
    Trace cur = par[n-1][m-1];
    string ans = "";
    while (1) {
        if (cur.c != '\0') ans += cur.c;
        if (!cur.i && !cur.j) break;
        cur = par[cur.i][cur.j];
    }
    reverse(all(ans));
    cout << ans;
}

#line 2 "template.h"

#include <bits/stdc++.h>
using namespace std;
 
#define ll long long
#define MOD (ll)(1e9+7)
#define all(x) (x).begin(),(x).end()
#define unique(x) x.erase(unique(all(x)), x.end())
#define INF32 ((1ull<<31)-1)
#define INF64 ((1ull<<63)-1)
#define inf (ll)1e18

#define vi vector<int>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second

const int mod = 998244353;

void solve();

int main(){
    ios_base::sync_with_stdio(false);cin.tie(NULL);
    // cin.exceptions(cin.failbit);
    // int t; cin >> t;
    // while(t--)
        solve();
    cerr << "\nTime run: " << 1000 * clock() / CLOCKS_PER_SEC << "ms" << '\n';
    return 0;
}
#line 2 "Dp/LCS.h"


// Longest common substring with trace

struct Trace {
    int i, j;
    char c;
    Trace(int _i = 0, int _j = 0, char _c = '\0'): i(_i), j(_j), c(_c) {}
};

void solve() {
    string s1, s2; cin >> s1 >> s2;
    s1 = "#" + s1;
    s2 = "#" + s2;
    int n = s1.size(), m = s2.size();
    int dp[n][m];
    Trace par[n][m] = {};
    memset(dp, 0, sizeof dp);
    for (int i = 1; i < n; i++) {
        for (int j = 1; j < m; j++) {
            if (s1[i] == s2[j]) {
                dp[i][j] = dp[i-1][j-1] + 1;
                par[i][j] = Trace(i-1, j-1, s1[i]);
            } else {
                if (dp[i][j-1] >= dp[i-1][j]) {
                    dp[i][j] = dp[i][j-1];
                    par[i][j] = Trace(i, j-1);
                } else {
                    dp[i][j] = dp[i-1][j];
                    par[i][j] = Trace(i-1, j);
                }
            }
        }
    }
    Trace cur = par[n-1][m-1];
    string ans = "";
    while (1) {
        if (cur.c != '\0') ans += cur.c;
        if (!cur.i && !cur.j) break;
        cur = par[cur.i][cur.j];
    }
    reverse(all(ans));
    cout << ans;
}

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