01.06. Compress String

class Solution:
    def compressString(self, S: str) -> str:
        if len(S) < 2:
            return S
        p, q = 0, 1
        res = ''
        while q < len(S):
            if S[p] != S[q]:
                res += (S[p] + str(q - p))
                p = q
            q += 1
        res += (S[p] + str(q - p))
        return res if len(res) < len(S) else S

class Solution {
    public String compressString(String S) {
        int n;
        if (S == null || (n = S.length()) < 2) {
            return S;
        }
        int p = 0, q = 1;
        StringBuilder sb = new StringBuilder();
        while (q < n) {
            if (S.charAt(p) != S.charAt(q)) {
                sb.append(S.charAt(p)).append(q - p);
                p = q;
            }
            ++q;
        }
        sb.append(S.charAt(p)).append(q - p);
        String res = sb.toString();
        return res.length() < n ? res : S;
    }
}

/**
 * @param {string} S
 * @return {string}
 */
var compressString = function (S) {
    if (!S) return S;
    let p = 0,
        q = 1;
    let res = "";
    while (q < S.length) {
        if (S[p] != S[q]) {
            res += S[p] + (q - p);
            p = q;
        }
        ++q;
    }
    res += S[p] + (q - p);
    return res.length < S.length ? res : S;
};

func compressString(S string) string {
	n := len(S)
	if n == 0 {
		return S
	}
	var builder strings.Builder
	pre, cnt := S[0], 1
	for i := 1; i < n; i++ {
		if S[i] != pre {
			builder.WriteByte(pre)
			builder.WriteString(strconv.Itoa(cnt))
			cnt = 1
		} else {
			cnt++
		}
		pre = S[i]
	}
	builder.WriteByte(pre)
	builder.WriteString(strconv.Itoa(cnt))
	if builder.Len() >= n {
		return S
	}
	return builder.String()
}