From 9f4193858fc53998dab02bf1893fb1abefe96957 Mon Sep 17 00:00:00 2001
From: Sainnhe Park <i@sainnhe.dev>
Date: Tue, 15 Nov 2022 16:54:39 +0800
Subject: [PATCH] s0029

---
 include/s0029_divide_two_integers.hpp | 11 ++++++++
 src/s0029_divide_two_integers.cpp     | 37 +++++++++++++++++++++++++++
 tests/s0029_divide_two_integers.cpp   | 19 ++++++++++++++
 3 files changed, 67 insertions(+)
 create mode 100644 include/s0029_divide_two_integers.hpp
 create mode 100644 src/s0029_divide_two_integers.cpp
 create mode 100644 tests/s0029_divide_two_integers.cpp

diff --git a/include/s0029_divide_two_integers.hpp b/include/s0029_divide_two_integers.hpp
new file mode 100644
index 0000000..b78f606
--- /dev/null
+++ b/include/s0029_divide_two_integers.hpp
@@ -0,0 +1,11 @@
+#ifndef S0029_DIVIDE_TWO_INTEGERS
+#define S0029_DIVIDE_TWO_INTEGERS
+
+#include <climits>
+
+class Solution {
+ public:
+  int divide(int dividend, int divisor);
+};
+
+#endif
diff --git a/src/s0029_divide_two_integers.cpp b/src/s0029_divide_two_integers.cpp
new file mode 100644
index 0000000..618836f
--- /dev/null
+++ b/src/s0029_divide_two_integers.cpp
@@ -0,0 +1,37 @@
+#include "s0029_divide_two_integers.hpp"
+
+// 举个例子：11 除以 3 。
+// 首先11比3大，结果至少是1，
+// 然后我让3翻倍，就是6，发现11比3翻倍后还要大，那么结果就至少是2了，那我让这个6再翻倍，得12，11不比12大，吓死我了，差点让就让刚才的最小解2也翻倍得到4了。但是我知道最终结果肯定在2和4之间。也就是说2再加上某个数，这个数是多少呢？我让11减去刚才最后一次的结果6，剩下5，我们计算5是3的几倍，也就是除法，看，递归出现了。
+
+int div(long a, long b) {  // 似乎精髓和难点就在于下面这几句
+  if (a < b) return 0;
+  long count = 1;
+  long tb = b;  // 在后面的代码中不更新b
+  while ((tb + tb) <= a) {
+    count = count + count;  // 最小解翻倍
+    tb = tb + tb;           // 当前测试的值也翻倍
+  }
+  return count + div(a - tb, b);
+}
+
+int Solution::divide(int dividend, int divisor) {
+  if (dividend == 0) return 0;
+  if (divisor == 1) return dividend;
+  if (divisor == -1) {
+    if (dividend > INT_MIN)
+      return -dividend;  // 只要不是最小的那个整数，都是直接返回相反数就好啦
+    return INT_MAX;  // 是最小的那个，那就返回最大的整数啦
+  }
+  long a = dividend;
+  long b = divisor;
+  int sign = 1;
+  if ((a > 0 && b < 0) || (a < 0 && b > 0)) {
+    sign = -1;
+  }
+  a = a > 0 ? a : -a;
+  b = b > 0 ? b : -b;
+  long res = div(a, b);
+  if (sign > 0) return res > INT_MAX ? INT_MAX : res;
+  return -res;
+}
diff --git a/tests/s0029_divide_two_integers.cpp b/tests/s0029_divide_two_integers.cpp
new file mode 100644
index 0000000..c005832
--- /dev/null
+++ b/tests/s0029_divide_two_integers.cpp
@@ -0,0 +1,19 @@
+#include "s0029_divide_two_integers.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem29, Case1) {
+  int dividend{10};
+  int divisor{3};
+  int o{3};
+  Solution solution;
+  EXPECT_EQ(solution.divide(dividend, divisor), o);
+}
+
+TEST(Problem29, Case2) {
+  int dividend{7};
+  int divisor{-3};
+  int o{-2};
+  Solution solution;
+  EXPECT_EQ(solution.divide(dividend, divisor), o);
+}