P1439 【模板】最长公共子序列

本解法时间复杂度O(nlogn)O(nlogn)，还有一种 DP 的 O(n2)O(n^2) 的求法，感兴趣的可以上网了解一下

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#include<bits/stdc++.h>
using namespace std;
const int MAXn = 100000;
const int INF = 0x3f3f3f3f;

inline int read() {
    char c;
    while (c = getchar(), c < '0' || c>'9');
    int x(c - '0');
    while (c = getchar(), c >= '0' && c <= '9') x = x * 10 + c - '0';
    return x;
}

int id[MAXn + 10];
int mapping[MAXn + 10];
int d[MAXn + 10];
int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++)   id[read()] = i;
    for (int i = 1; i <= n; i++)   mapping[i] = id[read()];
    memset(d, 0x3f, sizeof(d));
    int len = 0;
    d[0] = 0;
    for (int i = 1; i <= n; i++) {
        int l = 0, r = len, mid;
        if (mapping[i] > d[len])   d[++len] = mapping[i];
        else {
            while (l < r) {
                mid = (l + r) / 2;
                if (d[mid] > mapping[i])   r = mid;
                else    l = mid + 1;
            }
            d[l] = min(mapping[i], d[l]);
        }
    }
    cout << len;
    return 0;
}