Leet Code 29 Divide Two Integers - 两个整数相除 - Java
2016-06-11 00:00
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摘要: Leet Code 29 Divide Two Integers - 两个整数相除 - Java
问题原始链接 https://leetcode.com/problems/divide-two-integers
不使用乘、除和模运算,实现两个整数相除。如果溢出,返回 MAX_INT。
第一种方法
被除数不断减去除数,如果能减则商加一,如果不能减,则结束。例如7除以2,初始商为0,首先7-2=5,商为0+1=1,然后5-2=3,商为1+1=2,再然后3-2=1,商为2+1=3,余数1不足以减2,结束,最后返回商为3。
时间复杂度O(被除数/除数)。
这种方法性能低,LeetCode性能超时。
第二种方法
设被除数为a,除数为b,假设a和b都是正整数,设商为q=0,首先找到整数n,使2^n*b<=a<=2^(n+1)*b,则q+=2^n,令a=a-2^n*b,然后如果a>=2^(n-1)*b则q+=2^(n-1)且令a=a-2^(n-1)*b,否则判断a与2^(n-1)*b的关系...
问题原始链接 https://leetcode.com/problems/divide-two-integers
不使用乘、除和模运算,实现两个整数相除。如果溢出,返回 MAX_INT。
第一种方法
被除数不断减去除数,如果能减则商加一,如果不能减,则结束。例如7除以2,初始商为0,首先7-2=5,商为0+1=1,然后5-2=3,商为1+1=2,再然后3-2=1,商为2+1=3,余数1不足以减2,结束,最后返回商为3。
时间复杂度O(被除数/除数)。
这种方法性能低,LeetCode性能超时。
[code=language-java]public class Solution { public static int divide(int dividend, int divisor) { if (divisor == 0) { throw new IllegalArgumentException("divisor can not be zero."); } if (dividend == 0) { return 0; } if (divisor == 1) { return dividend; } if (divisor == -1) { if (dividend == Integer.MIN_VALUE) { return Integer.MAX_VALUE; } return -dividend; } if (dividend > 0 && divisor > 0) { return divideBothNegative(-dividend, -divisor); } else if (dividend < 0 && divisor < 0) { return divideBothNegative(dividend, divisor); } else if (dividend < 0 && divisor > 0) { return -divideBothNegative(dividend, -divisor); } else { return -divideBothNegative(-dividend, divisor); } } private static int divideBothNegative(int dividend, int divisor) { int quotient = 0; while (dividend - divisor <= 0) { quotient++; dividend -= divisor; } return quotient; } }
第二种方法
设被除数为a,除数为b,假设a和b都是正整数,设商为q=0,首先找到整数n,使2^n*b<=a<=2^(n+1)*b,则q+=2^n,令a=a-2^n*b,然后如果a>=2^(n-1)*b则q+=2^(n-1)且令a=a-2^(n-1)*b,否则判断a与2^(n-1)*b的关系...
[code=language-java]public class Solution { private static int HALF_MIN_VALUE = Integer.MIN_VALUE >> 1; public static int divide(int dividend, int divisor) { if (divisor == 0) { throw new IllegalArgumentException("divisor can not be zero."); } if (dividend == 0) { return 0; } if (divisor == 1) { return dividend; } if (divisor == -1) { if (dividend == Integer.MIN_VALUE) { return Integer.MAX_VALUE; } return -dividend; } if (dividend > 0 && divisor > 0) { return divideBothNegative(-dividend, -divisor); } else if (dividend < 0 && divisor < 0) { return divideBothNegative(dividend, divisor); } else if (dividend < 0 && divisor > 0) { return -divideBothNegative(dividend, -divisor); } else { return -divideBothNegative(-dividend, divisor); } } private static int divideBothNegative(int dividend, int divisor) { if (dividend > divisor) { return 0; } if (dividend == divisor) { return 1; } int[] q = new int[31]; int[] d = new int[31]; q[0] = 1; d[0] = divisor; int i = 0; while (d[i] > dividend && d[i] >= HALF_MIN_VALUE) { i++; d[i] = d[i - 1] << 1; q[i] = q[i - 1] << 1; } int quotient = 0; while (dividend <= 0 && i >= 0) { if (dividend <= d[i]) { dividend -= d[i]; quotient += q[i]; } i--; } return quotient; } }
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