原题链接：Codeforces10D
题目大意：如题
LICS
因为需要输出方案，des记录最后一个位置，pre[]存前驱，des必须初始化为$0$，否则当LICS长度为$0$的时候，des不会被更新，dfs(des)就会RE。
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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
const int N = 510;
int n, m;
int a[N], b[N];
int f[N][N];
int pre[N];
void dfs(int u) {
if (!u) return;
dfs(pre[u]);
cout << b[u] << " ";
}
int main() {
cin >> n;
for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
cin >> m;
for (int i = 1; i <= m; i++) scanf("%d", &b[i]);
for (int i = 1; i <= n; i++) {
int maxv = 0, last = 0;
for (int j = 1; j <= m; j++) {
f[i][j] = f[i - 1][j];
if (a[i] == b[j]) {
if (f[i][j] < maxv + 1) {
f[i][j] = maxv + 1;
pre[j] = last;
}
}
if (b[j] < a[i]) {
if (f[i][j] > maxv) {
maxv = f[i][j];
last = j;
}
}
}
}
int res = 0, des = 0;
for (int i = 1; i <= m; i++) {
if (f[n][i] > res) {
res = max(res, f[n][i]);
des = i;
}
}
cout << res << endl;
dfs(des);
return 0;
}
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