专栏首页机器学习入门LWC 56:443. String Compression

LWC 56:443. String Compression

LWC 56:443. String Compression

传送门:443. String Compression

Problem:

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.

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:

All characters have an ASCII value in [35, 126].

1 <= len(chars) <= 1000.

思路: 非常暴力,按顺序计数即可,遇到不同重新归零,记录上一回合信息。

代码如下:

    public int compress(char[] chars) {
        int n = chars.length;

        if (n == 0) return 0;
        StringBuilder sb = new StringBuilder();

        char p = chars[0];
        int cnt = 1;
        for (int i = 1; i < n; ++i) {
            if (chars[i] == p) {
                cnt ++;
            }
            else {
                if (cnt == 1) {
                    sb.append(p);
                }
                else {
                    sb.append(p + "" + cnt);
                }
                cnt = 1;
            }
            p = chars[i];
        }

        if (cnt == 1) {
            sb.append(p);
        }
        else {
            sb.append(p + "" + cnt);
        }

        for (int i = 0; i < sb.length(); ++i) {
            chars[i] = sb.charAt(i);
        }

        return sb.length();
    }

优化一下:

    public int compress(char[] chars) {
        int n = chars.length;

        if (n == 0) return 0;

        char p = chars[0];
        int cnt = 1;
        int tot = 0;

        for (int i = 1; i < n; ++i) {
            if (chars[i] == p) {
                cnt ++;
            }
            else {
                if (cnt == 1) {
                    chars[tot++] = p;
                }
                else {
                    chars[tot++] = p;
                    String num = String.valueOf(cnt);
                    for (int j = 0; j < num.length(); ++j) {
                        chars[tot++] = num.charAt(j);
                    }
                }
                cnt = 1;
            }
            p = chars[i];
        }

        if (cnt == 1) {
            chars[tot++] = p;
        }
        else {
            chars[tot++] = p;
            String num = String.valueOf(cnt);
            for (int j = 0; j < num.length(); ++j) {
                chars[tot++] = num.charAt(j);
            }
        }

        return tot;
    }

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