// The rand7() API is already defined for you.
// int rand7();
// @return a random integer in the range 1 to 7
class Solution {
public:
int rand10() {
}
};
470. 用 Rand7() 实现 Rand10()
给定方法 rand7 可生成 [1,7] 范围内的均匀随机整数，试写一个方法 rand10 生成 [1,10] 范围内的均匀随机整数。
你只能调用 rand7() 且不能调用其他方法。请不要使用系统的 Math.random() 方法。
每个测试用例将有一个内部参数 n，即你实现的函数 rand10() 在测试时将被调用的次数。请注意，这不是传递给 rand10() 的参数。
示例 1:
输入: 1 输出: [2]
示例 2:
输入: 2 输出: [2,8]
示例 3:
输入: 3 输出: [3,8,10]
提示:
1 <= n <= 105
进阶:
rand7()调用次数的 期望值 是多少 ?rand7() ?原站题解
python3 解法, 执行用时: 276 ms, 内存消耗: 17.7 MB, 提交时间: 2022-12-08 12:01:29
# The rand7() API is already defined for you.
# def rand7():
# @return a random integer in the range 1 to 7
class Solution:
def rand10(self) -> int:
while True:
a = rand7()
b = rand7()
idx = (a - 1) * 7 + b
if idx <= 40:
return 1 + (idx - 1) % 10
a = idx - 40
b = rand7()
# get uniform dist from 1 - 63
idx = (a - 1) * 7 + b
if idx <= 60:
return 1 + (idx - 1) % 10
a = idx - 60
b = rand7()
# get uniform dist from 1 - 21
idx = (a - 1) * 7 + b
if idx <= 20:
return 1 + (idx - 1) % 10
golang 解法, 执行用时: 8 ms, 内存消耗: 5.5 MB, 提交时间: 2022-12-08 12:01:07
func rand10() int {
for {
a := rand7()
b := rand7()
idx := (a-1)*7 + b
if idx <= 40 {
return 1 + (idx-1)%10
}
a = idx - 40
b = rand7()
// get uniform dist from 1 - 63
idx = (a-1)*7 + b
if idx <= 60 {
return 1 + (idx-1)%10
}
a = idx - 60
b = rand7()
// get uniform dist from 1 - 21
idx = (a-1)*7 + b
if idx <= 20 {
return 1 + (idx-1)%10
}
}
}
javascript 解法, 执行用时: 88 ms, 内存消耗: 48.4 MB, 提交时间: 2022-12-08 12:00:54
/**
* The rand7() API is already defined for you.
* var rand7 = function() {}
* @return {number} a random integer in the range 1 to 7
*/
var rand10 = function() {
var a, b, idx;
while (true) {
a = rand7();
b = rand7();
idx = b + (a - 1) * 7;
if (idx <= 40) {
return 1 + (idx - 1) % 10;
}
a = idx - 40;
b = rand7();
// get uniform dist from 1 - 63
idx = b + (a - 1) * 7;
if (idx <= 60) {
return 1 + (idx - 1) % 10;
}
a = idx - 60;
b = rand7();
// get uniform dist from 1 - 21
idx = b + (a - 1) * 7;
if (idx <= 20) {
return 1 + (idx - 1) % 10;
}
}
};
java 解法, 执行用时: 5 ms, 内存消耗: 47.3 MB, 提交时间: 2022-12-08 12:00:37
/**
* The rand7() API is already defined in the parent class SolBase.
* public int rand7();
* @return a random integer in the range 1 to 7
*/
class Solution extends SolBase {
public int rand10() {
int a, b, idx;
while (true) {
a = rand7();
b = rand7();
idx = b + (a - 1) * 7;
if (idx <= 40) {
return 1 + (idx - 1) % 10;
}
a = idx - 40;
b = rand7();
// get uniform dist from 1 - 63
idx = b + (a - 1) * 7;
if (idx <= 60) {
return 1 + (idx - 1) % 10;
}
a = idx - 60;
b = rand7();
// get uniform dist from 1 - 21
idx = b + (a - 1) * 7;
if (idx <= 20) {
return 1 + (idx - 1) % 10;
}
}
}
}
java 解法, 执行用时: 5 ms, 内存消耗: 46.8 MB, 提交时间: 2022-12-08 11:59:27
/**
* The rand7() API is already defined in the parent class SolBase.
* public int rand7();
* @return a random integer in the range 1 to 7
*/
class Solution extends SolBase {
public int rand10() {
int row, col, idx;
do {
row = rand7();
col = rand7();
idx = col + (row - 1) * 7;
} while (idx > 40);
return 1 + (idx - 1) % 10;
}
}
javascript 解法, 执行用时: 72 ms, 内存消耗: 48.7 MB, 提交时间: 2022-12-08 11:59:13
/**
* The rand7() API is already defined for you.
* var rand7 = function() {}
* @return {number} a random integer in the range 1 to 7
*/
var rand10 = function() {
var row, col, idx;
do {
row = rand7();
col = rand7();
idx = col + (row - 1) * 7;
} while (idx > 40);
return 1 + (idx - 1) % 10;
};
golang 解法, 执行用时: 12 ms, 内存消耗: 5.5 MB, 提交时间: 2022-12-08 11:57:52
func rand10() int {
for {
row := rand7()
col := rand7()
idx := (row-1)*7 + col
if idx <= 40 {
return 1 + (idx-1)%10
}
}
}
python3 解法, 执行用时: 316 ms, 内存消耗: 17.5 MB, 提交时间: 2022-12-08 11:57:35
# The rand7() API is already defined for you.
# def rand7():
# @return a random integer in the range 1 to 7
class Solution:
def rand10(self) -> int:
while True:
row = rand7()
col = rand7()
idx = (row - 1) * 7 + col
if idx <= 40:
return 1 + (idx - 1) % 10