题目大意：给定两个大小为n的数组，让你找出最长公共上升子序列的长度。
分析：这是一个比较好的dp题，LIS和LCS两大经典线性dp问题相结合，简称LCIS。
代码（O（n*n*n）写法）：
#include<bits/stdc++.h> using namespace std; const int maxn = 3e3+7; int a[maxn],b[maxn]; int dp[maxn][maxn]; int main() { int n; cin >> n; for (int i = 1; i <= n; i++) cin >> a[i]; for (int i = 1; i <= n; i++) cin >> b[i]; a[0] = b[0] = -0x3f3f3f3f; for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) { if (a[i] == b[j]) { for (int k = 0; k < j; k++) { if (b[k] < a[i]) dp[i][j] = max(dp[i][j], dp[i - 1][k] + 1); } } else dp[i][j] = dp[i - 1][j]; } } int ans = 0; for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) { ans = max(ans, dp[i][j]); } } cout << ans << endl; return 0; }
代码（O（n*n）写法）：
#include<bits/stdc++.h> using namespace std; const int maxn = 3e3+7; int a[maxn],b[maxn]; int dp[maxn][maxn]; int main() { int n; cin >> n; for (int i = 1; i <= n; i++) cin >> a[i]; for (int i = 1; i <= n; i++) cin >> b[i]; a[0] = b[0] = -0x3f3f3f3f; for (int i = 1; i <= n; i++) { int val = 0; if (b[0] < a[i]) val = dp[i - 1][0]; for (int j = 1; j <= n; j++) { if (a[i] == b[j]) dp[i][j] = val + 1; else dp[i][j] = dp[i - 1][j]; if (b[j] < a[i]) val = max(val, dp[i - 1][j]); } } int ans = 0; for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) ans = max(ans, dp[i][j]); } cout << ans << endl; return 0; }