[LeetCode] 443. String Compression

轉自LeetCode

Given an array of characters, compress it in-place.

The length after compression must always be smaller than or equal to the original array.

Every element of the array should be a character (not int) of length 1.

After you are done modifying the input array in-place, return the new length of the array.

Follow up:
Could you solve it using only O(1) extra space?

Example 1:

Input:
["a","a","b","b","c","c","c"]

Output:
Return 6, and the first 6 characters of the input array should be: ["a","2","b","2","c","3"]

Explanation:
"aa" is replaced by "a2". "bb" is replaced by "b2". "ccc" is replaced by "c3".

Example 2:

Input:
["a"]

Output:
Return 1, and the first 1 characters of the input array should be: ["a"]

Explanation:
Nothing is replaced.

Example 3:

Input:
["a","b","b","b","b","b","b","b","b","b","b","b","b"]

Output:
Return 4, and the first 4 characters of the input array should be: ["a","b","1","2"].

Explanation:
Since the character "a" does not repeat, it is not compressed. "bbbbbbbbbbbb" is replaced by "b12".
Notice each digit has it's own entry in the array.

Note:

1. All characters have an ASCII value in [35, 126].
2. 1 <= len(chars) <= 1000.

<Solution>

想法如下(參考資料)

• 用三個指標，一個是寫的位置，一個是檢查的起始點，一個是檢查起始點之後的指標

• 當發現沒有重複的時候，將檢查起始點的字母寫進寫的位置，然後按順序寫入重複的次數

• 最後將檢查的起始點，更新到最後檢查的位置

code 如下

C++

	class Solution {
	public:
	int compress(vector<char>& chars) {
	const int len = chars.size();
	const int limit = len - 1;
	int writeIdx = 0, anchorIdx = 0;
	string str;
	for(int readIdx = 0; readIdx < len; readIdx++) {
	if(readIdx == limit || chars[readIdx] != chars[readIdx + 1]) {
	chars[writeIdx++] = chars[anchorIdx];
	if(readIdx > anchorIdx) {
	str = to_string(readIdx - anchorIdx + 1);
	for(const auto c : str) {
	chars[writeIdx++] = c;
	}
	}
	anchorIdx = readIdx+1;
	}
	}
	return writeIdx;
	}
	};

view raw stringCompression.cpp hosted with ❤ by GitHub

Java

	class Solution {
	public int compress(char[] chars) {
	final int limit = chars.length - 1;
	int writeIdx = 0, anchorIdx = 0;
	for(int readIdx = 0; readIdx < chars.length; readIdx++) {
	if(readIdx == limit || chars[readIdx] != chars[readIdx + 1]) {
	chars[writeIdx++] = chars[anchorIdx];
	if(readIdx > anchorIdx) {
	for(char c : ("" + (readIdx - anchorIdx + 1)).toCharArray()) {
	chars[writeIdx++] = c;
	}
	}
	anchorIdx = readIdx + 1;
	}
	}
	return writeIdx;
	}
	}

view raw stringCompression.java hosted with ❤ by GitHub