Given a palindromic string palindrome, replace exactly one character by any lowercase English letter so that the string becomes the lexicographically smallest possible string that isn’t a palindrome.
After doing so, return the final string. If there is no way to do so, return the empty string.
Example 1:
Input: palindrome = "abccba"
Output: "aaccba"
Example 2:
Input: palindrome = "a"
Output: ""
Constraints:
1 <= palindrome.length <= 1000
palindrome consists of only lowercase English letters.
Solution: Greedy
For the first half of the string, replace the first non ‘a’ character to ‘a’.
e.g. abcdcba => aacdcba
If not found which means the the entire string is ‘a’ expect the middle one if the length is odd, like aa or aba, replace the last character to ‘b’.
Given a positive integer num consisting only of digits 6 and 9.
Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).
Example 1:
Input: num = 9669
Output: 9969
Explanation:
Changing the first digit results in 6669.
Changing the second digit results in 9969.
Changing the third digit results in 9699.
Changing the fourth digit results in 9666.
The maximum number is 9969.
Example 2:
Input: num = 9996
Output: 9999
Explanation: Changing the last digit 6 to 9 results in the maximum number.
Example 3:
Input: num = 9999
Output: 9999
Explanation: It is better not to apply any change.
Constraints:
1 <= num <= 10^4
num‘s digits are 6 or 9.
Solution: Greedy
Replace the highest 6 to 9, if no 6, return the original number.
Given a binary tree root and an integer target, delete all the leaf nodes with value target.
Note that once you delete a leaf node with value target, if it’s parent node becomes a leaf node and has the value target, it should also be deleted (you need to continue doing that until you can’t).
Example 1:
Input: root = [1,2,3,2,null,2,4], target = 2
Output: [1,null,3,null,4]
Explanation: Leaf nodes in green with value (target = 2) are removed (Picture in left).
After removing, new nodes become leaf nodes with value (target = 2) (Picture in center).
There is a one-dimensional garden on the x-axis. The garden starts at the point 0 and ends at the point n. (i.e The length of the garden is n).
There are n + 1 taps located at points [0, 1, ..., n] in the garden.
Given an integer n and an integer array ranges of length n + 1 where ranges[i] (0-indexed) means the i-th tap can water the area [i - ranges[i], i + ranges[i]] if it was open.
Return the minimum number of taps that should be open to water the whole garden, If the garden cannot be watered return -1.
Example 1:
Input: n = 5, ranges = [3,4,1,1,0,0]
Output: 1
Explanation: The tap at point 0 can cover the interval [-3,3]
The tap at point 1 can cover the interval [-3,5]
The tap at point 2 can cover the interval [1,3]
The tap at point 3 can cover the interval [2,4]
The tap at point 4 can cover the interval [4,4]
The tap at point 5 can cover the interval [5,5]
Opening Only the second tap will water the whole garden [0,5]
Example 2:
Input: n = 3, ranges = [0,0,0,0]
Output: -1
Explanation: Even if you activate all the four taps you cannot water the whole garden.
Example 3:
Input: n = 7, ranges = [1,2,1,0,2,1,0,1]
Output: 3
Example 4:
Input: n = 8, ranges = [4,0,0,0,0,0,0,0,4]
Output: 2
Example 5:
Input: n = 8, ranges = [4,0,0,0,4,0,0,0,4]
Output: 1
