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Divide.java
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90 lines (75 loc) · 2.72 KB
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package Algorithms.binarySearch;
public class Divide {
public static void main(String[] strs) {
System.out.println(divide(-2147483648, -1));
}
public int divide1(int dividend, int divisor) {
long a = Math.abs((long)dividend);
// ref : http://blog.csdn.net/kenden23/article/details/16986763
// Note: 在这里必须先取long再abs，否则int的最小值abs后也是原值
long b = Math.abs((long)divisor);
int ret = 0;
// 这里必须是= 因为相等时也可以减
while (a >= b) {
// 判断条件是 >=
for (long deduce = b, cnt = 1; a >= deduce; deduce <<= 1, cnt <<= 1) {
a -= deduce;
ret += cnt;
}
}
// 获取符号位。根据除数跟被除数的关系来定
return (dividend > 0) ^ (divisor > 0) ? -ret: ret;
}
public static int divide(int dividend, int divisor) {
if (divisor == 0) {
return Integer.MAX_VALUE;
}
// Note: 在这里必须先取long再abs，否则int的最小值abs后也是原值
long dividendTmp = Math.abs((long)dividend);
long divisorTmp = Math.abs((long)divisor);
// bug 3: ret should use Long to avoid overflow.
long ret = 0;
// bug 2: should use dividentTmp > divisor as the while judge.
while (dividendTmp >= divisorTmp) {
// bug 1: should use Long for tmp.
long tmp = divisorTmp;
int rst = 1;
while(tmp <= dividendTmp) {
// bug 3: the two statement should inside the while LOOP.
ret += rst;
dividendTmp -= tmp;
tmp <<= 1;
rst <<= 1;
}
}
// bug 4: out of range:
/*
Input: -2147483648, -1
Output: -2147483648
Expected: 2147483647
*/
//ret = ((dividend > 0) ^ (divisor > 0)) ? -ret: ret;
ret = ((((dividend ^ divisor) >> 31) & 1) == 1) ? -ret: ret;
if (ret > Integer.MAX_VALUE || ret < Integer.MIN_VALUE) {
return Integer.MAX_VALUE;
} else {
return (int)ret;
}
}
public int divide3(int dividend, int divisor) {
long a = Math.abs((long)dividend);
long b = Math.abs((long)divisor);
long ret = 0;
while (a >= b) {
for (long tmp = b, cnt = 1; a >= tmp; tmp <<= 1, cnt <<= 1) {
ret += cnt;
a -= tmp;
}
}
ret = (((dividend ^ divisor) >> 31) & 1) == 1 ? -ret: ret;
if (ret > Integer.MAX_VALUE || ret < Integer.MIN_VALUE) {
return Integer.MAX_VALUE;
}
return (int)ret;
}
}