You are given a string s, consisting of n letters, each letter is either 'a' or 'b'. The letters in the string are numbered from 1 to n.

s[l;r] is a continuous substring of letters from index l to r of the string inclusive.

A string is called balanced if the number of letters 'a' in it is equal to the number of letters 'b'. For example, strings "baba" and "aabbab" are balanced and strings "aaab" and "b" are not.

Find any non-empty balanced substring s[l;r] of string s. Print its l and r (1≤l≤r≤n). If there is no such substring, then print ?1 ?1.

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給定一個(gè)字符串 s，由 n 個(gè)字母組成，每個(gè)字母要么是“a”，要么是“b”。 字符串中的字母從 1 到 n 編號(hào)。

s[l;r] 是字符串中從索引 l 到 r 的連續(xù)字母子串。

如果字符串中字母“a”的數(shù)量等于字母“b”的數(shù)量，則該字符串被稱為平衡字符串。 例如，字符串“baba”和“aabbab”是平衡的，而字符串“aaab”和“b”則不是。

查找字符串 s 的任意非空平衡子串 s[l;r]。 打印它的 l 和 r (1≤l≤r≤n)。 如果不存在這樣的子串，則打印?1 ?1。

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用presum來(lái)求和，然后依次去判斷即可；

下面是代碼：