处理int型整数运算时,为避免溢出,省事的做法就是内部转为long类型处理,不然极可能在极值case上栽跟头,比如int a = Integer.MIN_VALUE, int b = -1 和 long a = Integer.MIN_VALUE, long b = -1, 两者a / b的结果是不一样的,前者会发生溢出,
在比如Math.abs(Integer.MIN_VALUE) 结果竟然是Integer_MIN_VALUE,这都是各种Wrong Answer耐心地告诉我的。
实现2参考 https://leetcode.com/discuss/23079/my-clean-java-solution, 有条理的一步步构造出答案,觉得这种方式实现更不容易出错些,自己的实现1就犯过在判断符号后忘记讲intPart取绝对值导致的错误。
public class Solution { // especially take care of case like -2147483648 / -1 // Method 2 public String fractionToDecimal(int numerator, int denominator) { if (denominator == 0) return "Error: divide zero."; if (numerator == 0) return "0"; StringBuilder res = new StringBuilder(); res.append((numerator > 0 ^ denominator > 0) ? "-" : ""); long a = Math.abs((long)numerator); long b = Math.abs((long)denominator); //integer part res.append(a / b); long mod = a % b; if (mod == 0) return res.toString(); //fraction part res.append("."); HashMap<Long, Integer> map = new HashMap<Long, Integer>(); map.put(mod, res.length()); while (mod != 0) { mod *= 10; res.append(mod / b); mod %= b; if (map.containsKey(mod)) { res.insert(map.get(mod), "("); res.append(")"); break; } else { map.put(mod, res.length()); } } return res.toString(); } // Method 1 public String fractionToDecimal1(int numerator, int denominator) { long a = numerator, b = denominator; // Attention! if (b == 0) return "Divide zero exception."; long intPart = a / b; long mod = a % b; if (mod == 0) return String.valueOf(intPart); boolean isNeg = (a > 0 ^ b > 0) ? true : false; intPart = Math.abs(intPart); mod = Math.abs(mod); b = Math.abs(b); HashMap<Long, Integer> map = new HashMap<Long, Integer>(); StringBuilder fractionPart = new StringBuilder(); int i = 0; while (mod != 0 && !map.containsKey(mod)) { map.put(mod, i++); mod *= 10; fractionPart.append(mod / b); mod = mod % b; } if (mod == 0) { return (isNeg ? "-" : "") + intPart + "." + fractionPart.toString(); } else { int startRepeat = map.get(mod); return (isNeg ? "-" : "") + intPart + "." + fractionPart.substring(0, startRepeat) + "(" + fractionPart.substring(startRepeat, fractionPart.length()) + ")"; } } }