题目大意
略。
分析
先求 LCS 的 dp 表，然后倒着求 LCS。
代码如下
1 #include <bits/stdc++.h>
2 using namespace std;
3
4 #define INIT() ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
5 #define Rep(i,n) for (int i = 0; i < (int)(n); ++i)
6 #define For(i,s,t) for (int i = (int)(s); i <= (int)(t); ++i)
7 #define rFor(i,t,s) for (int i = (int)(t); i >= (int)(s); --i)
8 #define ForLL(i, s, t) for (LL i = LL(s); i <= LL(t); ++i)
9 #define rForLL(i, t, s) for (LL i = LL(t); i >= LL(s); --i)
10 #define foreach(i,c) for (__typeof(c.begin()) i = c.begin(); i != c.end(); ++i)
11 #define rforeach(i,c) for (__typeof(c.rbegin()) i = c.rbegin(); i != c.rend(); ++i)
12
13 #define pr(x) cout << #x << " = " << x << " "
14 #define prln(x) cout << #x << " = " << x << endl
15
16 #define LOWBIT(x) ((x)&(-x))
17
18 #define ALL(x) x.begin(),x.end()
19 #define INS(x) inserter(x,x.begin())
20 #define UNIQUE(x) x.erase(unique(x.begin(), x.end()), x.end())
21 #define REMOVE(x, c) x.erase(remove(x.begin(), x.end(), c), x.end()); // 删去 x 中所有 c
22 #define TOLOWER(x) transform(x.begin(), x.end(), x.begin(),::tolower);
23 #define TOUPPER(x) transform(x.begin(), x.end(), x.begin(),::toupper);
24
25 #define ms0(a) memset(a,0,sizeof(a))
26 #define msI(a) memset(a,0x3f,sizeof(a))
27 #define msM(a) memset(a,-1,sizeof(a))
28
29 #define MP make_pair
30 #define PB push_back
31 #define ft first
32 #define sd second
33
34 template<typename T1, typename T2>
35 istream &operator>>(istream &in, pair<T1, T2> &p) {
36 in >> p.first >> p.second;
37 return in;
38 }
39
40 template<typename T>
41 istream &operator>>(istream &in, vector<T> &v) {
42 for (auto &x: v)
43 in >> x;
44 return in;
45 }
46
47 template<typename T>
48 ostream &operator<<(ostream &out, vector<T> &v) {
49 Rep(i, v.size()) out << v[i] << " \n"[i == v.size() - 1];
50 return out;
51 }
52
53 template<typename T1, typename T2>
54 ostream &operator<<(ostream &out, const std::pair<T1, T2> &p) {
55 out << "[" << p.first << ", " << p.second << "]" << "\n";
56 return out;
57 }
58
59 inline int gc(){
60 static const int BUF = 1e7;
61 static char buf[BUF], *bg = buf + BUF, *ed = bg;
62
63 if(bg == ed) fread(bg = buf, 1, BUF, stdin);
64 return *bg++;
65 }
66
67 inline int ri(){
68 int x = 0, f = 1, c = gc();
69 for(; c<48||c>57; f = c=='-'?-1:f, c=gc());
70 for(; c>47&&c<58; x = x*10 + c - 48, c=gc());
71 return x*f;
72 }
73
74 template<class T>
75 inline string toString(T x) {
76 ostringstream sout;
77 sout << x;
78 return sout.str();
79 }
80
81 inline int toInt(string s) {
82 int v;
83 istringstream sin(s);
84 sin >> v;
85 return v;
86 }
87
88 //min <= aim <= max
89 template<typename T>
90 inline bool BETWEEN(const T aim, const T min, const T max) {
91 return min <= aim && aim <= max;
92 }
93
94 typedef unsigned int uI;
95 typedef long long LL;
96 typedef unsigned long long uLL;
97 typedef vector< int > VI;
98 typedef vector< bool > VB;
99 typedef vector< char > VC;
100 typedef vector< double > VD;
101 typedef vector< string > VS;
102 typedef vector< LL > VL;
103 typedef vector< VI > VVI;
104 typedef vector< VB > VVB;
105 typedef vector< VS > VVS;
106 typedef vector< VL > VVL;
107 typedef vector< VVI > VVVI;
108 typedef vector< VVL > VVVL;
109 typedef pair< int, int > PII;
110 typedef pair< LL, LL > PLL;
111 typedef pair< int, string > PIS;
112 typedef pair< string, int > PSI;
113 typedef pair< string, string > PSS;
114 typedef pair< double, double > PDD;
115 typedef vector< PII > VPII;
116 typedef vector< PLL > VPLL;
117 typedef vector< VPII > VVPII;
118 typedef vector< VPLL > VVPLL;
119 typedef vector< VS > VVS;
120 typedef map< int, int > MII;
121 typedef unordered_map< int, int > uMII;
122 typedef map< LL, LL > MLL;
123 typedef map< string, int > MSI;
124 typedef map< int, string > MIS;
125 typedef multiset< int > mSI;
126 typedef set< int > SI;
127 typedef stack< int > SKI;
128 typedef deque< int > DQI;
129 typedef queue< int > QI;
130 typedef priority_queue< int > PQIMax;
131 typedef priority_queue< int, VI, greater< int > > PQIMin;
132 const double EPS = 1e-8;
133 const LL inf = 0x7fffffff;
134 const LL infLL = 0x7fffffffffffffffLL;
135 const LL mod = 1e9 + 7;
136 const int maxN = 5e3 + 7;
137 const LL ONE = 1;
138 const LL evenBits = 0xaaaaaaaaaaaaaaaa;
139 const LL oddBits = 0x5555555555555555;
140
141 int N, M;
142 string str1, str2, ans;
143 // dp[i][j] 表示 str1 以 i 号字符结尾的前缀与 str2 以 j 号字符结尾的前缀的 LCS 长度
144 int dp[maxN][maxN];
145
146 void LCS() {
147 For(i, 1, N) {
148 For(j, 1, M) {
149 dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
150 if(str1[i] == str2[j]) dp[i][j] = max(dp[i][j], dp[i - 1][j - 1] + 1);
151 }
152 }
153 /*
154 For(i, 1, N) {
155 For(j, 1, M) {
156 cout << dp[i][j] << " ";
157 }
158 cout << endl;
159 }*/
160 }
161
162 void getAns() {
163 int i = N, j = M, len = dp[N][M];
164
165 while(i >= 0 && j >= 0 && len >= 0) {
166 if(dp[i][j] == dp[i][j - 1]) --j;
167 else if(dp[i][j] == dp[i - 1][j]) --i;
168 else {
169 ans[--len] = str1[i];
170 --i;
171 --j;
172 }
173 }
174 }
175
176 int main() {
177 //freopen("MyOutput.txt","w",stdout);
178 //freopen("input.txt","r",stdin);
179 //INIT();
180 cin >> str1 >> str2;
181 N = str1.size();
182 M = str2.size();
183 str1 = "#" + str1;
184 str2 = "#" + str2;
185 LCS();
186 if(dp[N][M]) {
187 ans.resize(dp[N][M]);
188 getAns();
189 cout << ans << endl;
190 }
191 else cout << -1 << endl;
192 return 0;
193 }