两数相除-中等

Author: Liu Jie

.gitignore

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+.idea

practice/divide_two_integers.py

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+#!/usr/bin/env python
+# coding=utf-8
+
+"""
+给定两个整数，被除数 dividend 和除数 divisor。将两数相除，要求不使用乘法、除法和 mod 运算符。
+
+返回被除数 dividend 除以除数 divisor 得到的商。
+
+来源：力扣（LeetCode）
+链接：https://leetcode-cn.com/problems/divide-two-integers
+著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
+"""
+
+
+def divide(dividend, divisor):
+    is_negative = (dividend < 0) != (divisor < 0)
+    if dividend < 0:
+        dividend = -dividend
+    if divisor < 0:
+        divisor = -divisor
+
+    i = 0
+    step = divisor
+    step_count = 1
+    begin_reduce = False
+
+    step_list = []
+    index = 0
+    while dividend >= divisor:
+
+        # print(dividend, step)
+        while dividend < step and index >= 0:
+            step, step_count = step_list[index]
+            index -= 1
+
+        if index < 0 and dividend < step:
+            break
+
+        dividend -= step
+        i += step_count
+
+        if not begin_reduce:
+            step_list.append((step, step_count))
+            step += step
+            step_count += step_count
+            index = len(step_list) - 1
+
+    if is_negative:
+        return max(-i, -1 << 31)
+    return min(i, (1 << 31) - 1)
+
+
+def main():
+    cases = [
+        (10, 3, 3),
+        (7, -3, -2),
+        (4294967296, -1, -2147483648)
+    ]
+
+    for dd, dr, r in cases:
+        result = divide(dd, dr)
+        if result != r:
+            print('{} / {} != {}, {}'.format(dd, dr, result, r))
+            exit(-1)
+    print('pass')
+
+
+if __name__ == '__main__':
+    main()