leetcode-8-String to Integer (atoi)
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问题
题目:[leetcode-8]
思路
说下思路,虽然做了一个半小时。不过思路基本上一直都是正确的。这个题目应该反复写下,应为要考虑的情形是比较多的。大的思路是找到第一个pattern出来,然后围绕这个pattern处理。主要处理三部分逻辑:
- 抽出pattern
- 符号处理
- 越界
代码
class Solution {public: int myAtoi(string str) { int sz = str.size(); if(!sz) return 0; string s; if( !pattern(str, s) ) return 0; //std::cout << s << std::endl; sz = s.size(); if(!sz) return 0; if(1==sz && (s[0]=='+' || s[0]=='-')) return 0; int flag = 1; if(s[0]=='+' || s[0]=='-'){ if(s[0]=='-') flag = 0; s = string(s.begin() + 1, s.end()); } //std::cout << "before string2int : " << s << std::endl; if(s.size() > 10) { if(flag) return INT_MAX; else return INT_MIN; } const string MAX = "2147483647"; const string MIN = "2147483648"; if(flag && 10 == s.size() && s > MAX) return INT_MAX; if(!flag && 10 == s.size() && s > MIN) return INT_MIN; unsigned int ans = string2int(s); return flag?ans:-1*ans; }private: bool pattern( string& str, string& out ){ string::iterator b = find_if( str.begin(), str.end(), legal ); if( !legal1(*b) ) return false; string::iterator e = find_if( b+1, str.end(), illegal ); out = string(b, e); return true; } unsigned int string2int(string s){ stringstream ss(s); unsigned int val; ss >> val; return val; }private: static bool legal( char ch ) { return !isspace(ch); } static bool illegal( char ch ) { return !isdigit(ch); } static bool legal1( char ch ){ return ch=='+' || ch=='-' || isdigit(ch); }};
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