You are given a string num
, which represents a large integer. You are also given a 0-indexed integer array change
of length 10
that maps each digit 0-9
to another digit. More formally, digit d
maps to digit change[d]
.
You may choose to mutate any substring of num
. To mutate a substring, replace each digit num[i]
with the digit it maps to in change
(i.e. replace num[i]
with change[num[i]]
).
Return a string representing the largest possible integer after mutating (or choosing not to) any substring of num
.
A substring is a contiguous sequence of characters within the string.
Example 1:
Input: num = "132", change = [9,8,5,0,3,6,4,2,6,8] Output: "832" Explanation: Replace the substring "1": - 1 maps to change[1] = 8. Thus, "132" becomes "832". "832" is the largest number that can be created, so return it.
Example 2:
Input: num = "021", change = [9,4,3,5,7,2,1,9,0,6] Output: "934" Explanation: Replace the substring "021": - 0 maps to change[0] = 9. - 2 maps to change[2] = 3. - 1 maps to change[1] = 4. Thus, "021" becomes "934". "934" is the largest number that can be created, so return it.
Example 3:
Input: num = "5", change = [1,4,7,5,3,2,5,6,9,4] Output: "5" Explanation: "5" is already the largest number that can be created, so return it.
Constraints:
1 <= num.length <= 105
num
consists of only digits0-9
.change.length == 10
0 <= change[d] <= 9
Intuition: Try to change the digit from left to right. We only greedily make the change if we can make it greater or the same.
Algorithm:
One caveat is that, we should skip the leading digits if making changes won't result in greater digit. So we can keep track of a boolean changed
indicating whether we have made changes.
If we haven't made any changes:
- If the change results in a greater digit, we do it.
- Otherwise, we just skip the digit.
If we have made changes:
- If the change results in a greater or equal digit, we do it.
- Otherwise, we should stop the loop.
// OJ: https://leetcode.com/problems/largest-number-after-mutating-substring/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
string maximumNumber(string num, vector<int>& A) {
bool changed = false;
for (char &c : num) {
int before = c - '0', after = A[before];
if (after < before) {
if (changed) break;
continue;
} else if (after == before) {
continue;
}
changed = true;
c = '0' + after;
}
return num;
}
};
Or
// OJ: https://leetcode.com/problems/largest-number-after-mutating-substring/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
string maximumNumber(string num, vector<int>& A) {
bool changed = false;
for (char &c : num) {
int before = c - '0', after = A[before];
if (changed) {
if (after >= before) c = '0' + after;
else break;
} else {
if (after > before) {
c = '0' + after;
changed = true;
}
}
}
return num;
}
};