<p>Given two integer arrays&nbsp;<code>arr1</code> and <code>arr2</code>, return the minimum number of operations (possibly zero) needed&nbsp;to make <code>arr1</code> strictly increasing.</p>

<p>In one operation, you can choose two indices&nbsp;<code>0 &lt;=&nbsp;i &lt; arr1.length</code>&nbsp;and&nbsp;<code>0 &lt;= j &lt; arr2.length</code>&nbsp;and do the assignment&nbsp;<code>arr1[i] = arr2[j]</code>.</p>

<p>If there is no way to make&nbsp;<code>arr1</code>&nbsp;strictly increasing,&nbsp;return&nbsp;<code>-1</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> arr1 = [1,5,3,6,7], arr2 = [1,3,2,4]
<strong>Output:</strong> 1
<strong>Explanation:</strong> Replace <code>5</code> with <code>2</code>, then <code>arr1 = [1, 2, 3, 6, 7]</code>.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> arr1 = [1,5,3,6,7], arr2 = [4,3,1]
<strong>Output:</strong> 2
<strong>Explanation:</strong> Replace <code>5</code> with <code>3</code> and then replace <code>3</code> with <code>4</code>. <code>arr1 = [1, 3, 4, 6, 7]</code>.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> arr1 = [1,5,3,6,7], arr2 = [1,6,3,3]
<strong>Output:</strong> -1
<strong>Explanation:</strong> You can&#39;t make <code>arr1</code> strictly increasing.</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= arr1.length, arr2.length &lt;= 2000</code></li>
	<li><code>0 &lt;= arr1[i], arr2[i] &lt;= 10^9</code></li>
</ul>

<p>&nbsp;</p>

class Solution {
    int helper(vector<int>& arr1, vector<int>& arr2, int prev, int index, unordered_map<int, vector<int>> &m) {
        // base case
        if (index == arr1.size())
            return 0;

        if (m.find(prev) == m.end()) {
            m[prev] = vector<int>(arr1.size(), -1);
        }
        if (m[prev][index] != -1) {
            return m[prev][index];
        }

        int noreplace = INT_MAX, replace = INT_MAX;
        auto ub = upper_bound(arr2.begin(), arr2.end(), prev);

        if (ub != arr2.end()) {
            int temp = arr1[index];
            arr1[index] = *ub;
            replace = helper(arr1, arr2, arr1[index], index + 1, m);
            if (replace != INT_MAX)
                replace++;
            arr1[index] = temp;
        }

        if (prev < arr1[index]) {
            noreplace = helper(arr1, arr2, arr1[index], index + 1, m);
        }
        return m[prev][index] = min(noreplace, replace);
    }
public:
    int makeArrayIncreasing(vector<int>& arr1, vector<int>& arr2) {
        unordered_map<int, vector<int>> m;
        vector<int> spare;
        sort(arr2.begin(), arr2.end());
        spare.push_back(arr2[0]);
        for (int i = 1; i < arr2.size(); i++) {
            if (spare.back() == arr2[i])
                continue;
            spare.push_back(arr2[i]);
        }
        int answer = helper(arr1, spare, -1, 0, m);
        return answer == INT_MAX ? -1 : answer;
    }
};
65653