In a string S of lowercase letters, these letters form consecutive groups of the same character.
For example, a string like S = "abbxxxxzyy" has the groups "a", "bb", "xxxx", "z" and "yy".
Call a group large if it has 3 or more characters. We would like the starting and ending positions of every large group.
The final answer should be in lexicographic order.
Example 1:
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| Input: "abbxxxxzzy"
Output: [[3,6]]
Explanation: "xxxx" is the single large group with starting 3 and ending positions 6.
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Example 2:
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| Input: "abc"
Output: []
Explanation: We have "a","b" and "c" but no large group.
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Example 3:
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| Input: "abcdddeeeeaabbbcd"
Output: [[3,5],[6,9],[12,14]]
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双指针
感觉不难, 直接双指针即可. 别忘了最后退出循环之后还要再判断一次最后的Group是不是LargeGroup.
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| class Solution {
public:
vector<vector<int>> largeGroupPositions(string S) {
vector<vector<int>> vvc;
int begin = 0;
int end = 0;
while(end != S.size())
{
if(S[end] == S[begin])
++end;
else
{
int groupLen = end - begin;
if(groupLen >= 3)
vvc.push_back(vector<int>({begin,end - 1}));
begin = end;
}
}
assert(end == S.size());
int groupLen = end - begin;
if(groupLen >= 3)
vvc.push_back(vector<int>({begin,end - 1}));
return vvc;
}
};
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