LeetCode 2407. 最长递增子序列 II

LeetCode 2407. 最长递增子序列 II

线段树

struct Node
{
    int l, r, v;
};
vector<Node> tr;
void build(int u, int l, int r)
{
    tr[u] = {l, r};
    if(l == r) return;
    int mid = (l + r) >> 1;
    build(u << 1, l, mid), build(u << 1 | 1, mid + 1, r);
}
void pushup(int u)
{
    tr[u].v = max(tr[u << 1].v, tr[u << 1 | 1].v);
}
void modify(int u, int x, int v)
{
    if(tr[u].l == x && tr[u].r == x) tr[u].v = v;
    else
    {
        int mid = (tr[u].l + tr[u].r) >> 1;
        if(x <= mid) modify(u << 1, x, v);
        else modify(u << 1 | 1, x, v);
        pushup(u);
    }
}
int query(int u, int l, int r)
{
    if(tr[u].l >= l && tr[u].r <= r) return tr[u].v;
    int mid = (tr[u].l + tr[u].r) >> 1;
    int v = 0;
    if(l <= mid) v = query(u << 1, l, r);
    if(r > mid) v = max(v, query(u << 1 | 1, l, r));
    return v;
}
class Solution {
public:
    int lengthOfLIS(vector<int>& nums, int k) {
        int n = *max_element(nums.begin(), nums.end());
        tr.resize(4 * n);
        build(1, 1, n);
        for(auto&& x : nums)
        {
            if(x == 1) modify(1, 1, 1);
            else
            {
                int res = query(1, max(1, x - k), x - 1) + 1;
                // cout << res << endl;
                modify(1, x, res);
            }
        }
        return tr[1].v;
    }
};
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