题目 #

You are given a binary string s consisting only of zeroes and ones.

A substring of s is considered balanced if all zeroes are before ones and the number of zeroes is equal to the number of ones inside the substring. Notice that the empty substring is considered a balanced substring.

Return the length of the longest balanced substring of s.

A substring is a contiguous sequence of characters within a string.

Example 1:

Input: s = "01000111"
Output: 6
Explanation: The longest balanced substring is "000111", which has length 6.

Example 2:

Input: s = "00111"
Output: 4
Explanation: The longest balanced substring is "0011", which has length 4.

Example 3:

Input: s = "111"
Output: 0
Explanation: There is no balanced substring except the empty substring, so the answer is 0.

Constraints:

• 1 <= s.length <= 50
• ‘0’ <= s[i] <= ‘1’

思路1 #

分析 #

• 遍历一遍，对每一组01进行统计，在1到0的时候更新最大值

代码 #

 1func max(a, b int) int {
 2	if a < b {
 3		return b
 4	}
 5	return a
 6}
 7
 8func min(a, b int) int {
 9	if a > b {
10		return b
11	}
12	return a
13}
14
15func findTheLongestBalancedSubstring(s string) int {
16	res := 0
17	pre, cnt := 0, 0 // pre为0的数量，cnt为当前字符连续的数量
18	n := len(s)
19	for i, v := range s {
20		cnt++
21		if i == n-1 || byte(v) != s[i+1] {
22			if v == '0' {
23				// 0到1变化，pre等于cnt
24				pre = cnt
25			} else {
26				// 1到0变化，判断是否可以更新res
27				res = max(res, min(pre, cnt)*2)
28			}
29			// 变化重新统计
30			cnt = 0
31		}
32	}
33	return res
34}