1187. Make Array Strictly Increasing

Problem Link

Description

---

Given two integer arrays arr1 and arr2, return the minimum number of operations (possibly zero) needed to make arr1 strictly increasing.

In one operation, you can choose two indices 0 <= i < arr1.length and 0 <= j < arr2.length and do the assignment arr1[i] = arr2[j].

If there is no way to make arr1 strictly increasing, return -1.

 

Example 1:

Input: arr1 = [1,5,3,6,7], arr2 = [1,3,2,4]
Output: 1
Explanation: Replace 5 with 2, then arr1 = [1, 2, 3, 6, 7].

Example 2:

Input: arr1 = [1,5,3,6,7], arr2 = [4,3,1]
Output: 2
Explanation: Replace 5 with 3 and then replace 3 with 4. arr1 = [1, 3, 4, 6, 7].

Example 3:

Input: arr1 = [1,5,3,6,7], arr2 = [1,6,3,3]
Output: -1
Explanation: You can't make arr1 strictly increasing.

 

Constraints:

• 1 <= arr1.length, arr2.length <= 2000
• 0 <= arr1[i], arr2[i] <= 10^9

 

Solution

---

Python3

class Solution:
    def makeArrayIncreasing(self, arr1: List[int], arr2: List[int]) -> int:
        M, N = len(arr1), len(arr2)
        arr2.sort()
 
        @cache
        def go(i, prev):
            if i == M: return 0
 
            j = bisect_right(arr2, prev)
 
            res = inf
 
            if j < N:
                res = min(res, 1 + go(i + 1, arr2[j]))
            
            if prev < arr1[i]:
                res = min(res, go(i + 1, arr1[i]))
 
            return res
        
        res = go(0, -inf)
 
        return -1 if res == inf else res