Solution.java

class Solution {
    public int lengthOfLIS(int[] nums, int k) {
        int mx = nums[0];
        for (int v : nums) {
            mx = Math.max(mx, v);
        }
        SegmentTree tree = new SegmentTree(mx);
        int ans = 0;
        for (int v : nums) {
            int t = tree.query(1, v - k, v - 1) + 1;
            ans = Math.max(ans, t);
            tree.modify(1, v, t);
        }
        return ans;
    }
}

class Node {
    int l;
    int r;
    int v;
}

class SegmentTree {
    private Node[] tr;

    public SegmentTree(int n) {
        tr = new Node[4 * n];
        for (int i = 0; i < tr.length; ++i) {
            tr[i] = new Node();
        }
        build(1, 1, n);
    }

    public void build(int u, int l, int r) {
        tr[u].l = l;
        tr[u].r = r;
        if (l == r) {
            return;
        }
        int mid = (l + r) >> 1;
        build(u << 1, l, mid);
        build(u << 1 | 1, mid + 1, r);
    }

    public void modify(int u, int x, int v) {
        if (tr[u].l == x && tr[u].r == x) {
            tr[u].v = v;
            return;
        }
        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);
    }

    public void pushup(int u) {
        tr[u].v = Math.max(tr[u << 1].v, tr[u << 1 | 1].v);
    }

    public 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 = Math.max(v, query(u << 1 | 1, l, r));
        }
        return v;
    }
}