标签：false for ide hid ref val catch 开始 循环
这个题很简单的.最开始的想法是trim一下去掉开头的空格.然后放到字符串中,转成整数.
public static int myAtoi(String str) { StringBuilder res = new StringBuilder(""); StringBuilder str2 = new StringBuilder(""); int n = str.length(); int len=0; char c ; boolean flag = false; boolean lzero = false; for(int i=0;i<n;i++){ c = str.charAt(i); if(flag==false&&c==‘ ‘) continue; if(flag==false&&c!=‘ ‘){ flag=true; str2.append(c); len++; continue; } str2.append(c); len++; } //str = str.trim(); flag=false; for(int i=0;i<len;i++){ c = str2.charAt(i); if(c==‘+‘){ if(flag==false) { flag = true; continue; } break; } if(c==‘-‘){ if(flag==false){ flag=true; res.append(c); continue; } break; }else if(‘0‘<=c&&c<=‘9‘){ res.append(c); flag=true; continue; }else{ break; //if(c==‘ ‘) continue; } } if(res.length()==0) return 0; if(res.length()==1){ c = res.charAt(0); if(c==‘-‘||c==‘+‘) return 0; } try { return Integer.parseInt(res.toString()); }catch (Exception e){ if(res.charAt(0)==‘-‘) return Integer.MIN_VALUE; else return Integer.MAX_VALUE; }
然后发现大佬可以更快的执行,想了一下,可以一遍循环做完不用trim.但是效果不明显,也就是5ms和4ms的区别.
public static int myAtoi2(String str) { StringBuilder res = new StringBuilder(""); StringBuilder str2 = new StringBuilder(""); int n = str.length(); int len=0; char c ; boolean flag = false; boolean lzero = false; for(int i=0;i<n;i++){ c = str.charAt(i); if(c==‘ ‘&&len==0) continue; if(c==‘+‘||c==‘-‘){ if(len==0){ res.append(c); len++; continue; } break; } if(c>=‘0‘&&c<=‘9‘){ res.append(c); len++; continue; } break; } if(len==0) return 0; if(len==1){ c = res.charAt(0); if(c==‘-‘||c==‘+‘) return 0; } try { return Integer.parseInt(res.toString()); }catch (Exception e){ if(res.charAt(0)==‘-‘) return Integer.MIN_VALUE; else return Integer.MAX_VALUE; }
接着考虑,不用Interger转换,直接计算转换的值.这样可3ms
StringBuilder res = new StringBuilder(""); StringBuilder str2 = new StringBuilder(""); int n = str.length(); int len = 0; int ans = 0; long tmp = 0; char c; boolean flag = false; boolean lzero = false; for (int i = 0; i < n; i++) { c = str.charAt(i); if ((c == ‘ ‘ )&& len == 0) continue; if (c == ‘+‘ || c == ‘-‘) { if (len == 0) { if (c == ‘-‘) lzero = true; res.append(c); len++; continue; } break; } if (c >= ‘0‘ && c <= ‘9‘) { res.append(c); len++; int a = lzero ? (-(c - ‘0‘)) : (c - ‘0‘); tmp = tmp * 10 + a; if(tmp>Integer.MAX_VALUE) return Integer.MAX_VALUE; if(tmp<Integer.MIN_VALUE) return Integer.MIN_VALUE; ans = (int)tmp; continue; } break; } return ans; }
注意:我们用long型的数据保存temp,暂存这个值,然后比较它是否大于整型的最大存储范围..这个地方比较难想到...
标签：false for ide hid ref val catch 开始 循环
原文地址：https://www.cnblogs.com/superxuezhazha/p/12590019.html
