从两个可能的值中为变量指定另一个值
假设一个变量 x 只能有两个可能的值 a 和 b，并且您希望将当前值以外的值赋给 x。在不使用任何条件运算符的情况下高效地执行。 注意:我们不允许检查 x 的当前值。 示例:
输入:a = 10，b = 15，x = a 输出:x = 15 解释 x = 10，目前 x 有 a 的值(也就是 10)，我们需要改成 15。 输入:a = 9，b = 11，x = b 输出:x = 9
我们可以用 if 条件来解决这个问题，但是我们不能这么做。
if (x == a)
x = b;
else x = a;
我们可以使用三元运算符，它也检查 x 的当前值，并在此基础上分配新值。所以我们也不能使用这种方法
x = x == a ? b : a;
但是，我们不允许检查 x 的值，所以上述解决方案都不起作用。 解决方案 1: 仅使用算术运算符，我们可以执行此操作
x = a + b - x
这样，x 的内容将在每次执行时在 a 和 b 之间交替
C++
// CPP program to change value of x
// according to its current value.
#include <bits/stdc++.h>
using namespace std;
// Function to alternate the values
void alternate(int& a, int& b, int& x)
{
x = a + b - x;
}
// Main function
int main()
{
int a = -10;
int b = 15;
int x = a;
cout << "x is : " << x;
alternate(a, b, x);
cout << "\nAfter change ";
cout << "\nx is : " << x;
}
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to change value of x
// according to its current value.
import java.util.*;
class solution
{
// Function to alternate the values
static void alternate(int a, int b, int x)
{
x = a + b - x;
System.out.println("After change"+"\n"+" x is : "+x);
}
// Main function
public static void main(String args[])
{
int a = -10;
int b = 15;
int x = a;
System.out.println("x is : "+x);
alternate(a, b, x);
}
}
Python 3
# Python3 program to change value
# of x according to its current value.
# Function to alternate the values
def alternate(a,b,x):
x = a+b-x
print("After change x is:",x)
# Driver code
if __name__=='__main__':
a = -10
b = 15
x = a
print("x is:",x)
alternate(a,b,x)
# This code is contributed by
# Shrikant13
C
// C# program to change value of x
// according to its current value.
using System;
class gfg
{
// Function to alternate the values
public void alternate(ref int a, ref int b, ref int x)
//'ref' indicates the references
{
x = a + b - x;
}
}
// Main function
class geek
{
public static int Main()
{
gfg g = new gfg();
int a = -10;
int b = 15;
int x = a;
Console.WriteLine("x is : {0}" , x);
g.alternate(ref a, ref b, ref x);
Console.WriteLine ("After change ");
Console.WriteLine("x is : {0}", x);
return 0;
}
}
//This code is contributed by Soumik
服务器端编程语言（Professional Hypertext Preprocessor 的缩写）
<?php
// PHP program to change value of x
// according to its current value.
// Function to alternate the values
function alternate (&$a, &$b, &$x)
{
$x = $a + $b - $x;
}
// Driver Code
$a = -10;
$b = 15;
$x = $a;
echo "x is : ", $x;
alternate($a, $b, $x);
echo "\nAfter change ";
echo "\nx is : ", $x;
// This code is contributed by ajit.
?>
java 描述语言
<script>
// javascript program to change value of x
// according to its current value.
// Function to alternate the values
function alternate(a , b , x) {
x = a + b - x;
document.write("After change" + "<br/>" + " x is : " + x);
}
// Main function
var a = -10;
var b = 15;
var x = a;
document.write("x is : " + x+"<br/>");
alternate(a, b, x);
// This code is contributed by todaysgaurav
</script>
Output:
x is : -10
After change
x is : 15
时间复杂度:该方法的时间复杂度为 O(1) 空间复杂度:该方法的空间复杂度为 O(1) 解决方案 2: 一种更好更有效的方法是使用按位异或运算。 x = a^b^x
C++
// CPP program to change value of x
// according to its current value.
#include <bits/stdc++.h>
using namespace std;
// Function to alternate the values
void alternate(int& a, int& b, int& x)
{
x = a ^ b ^ x;
}
// Main function
int main()
{
int a = -10;
int b = 15;
int x = a;
cout << "x is : " << x;
alternate(a, b, x);
cout << "\nAfter exchange ";
cout << "\nx is : " << x;
return 0;
}
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to change value of x
// according to its current value.
class GFG {
// Function to alternate the values
static int alternate(int a, int b, int x) {
return x = a ^ b ^ x;
}
// Main function
public static void main(String[] args) {
int a = -10;
int b = 15;
int x = a;
System.out.print("x is : " + x);
x = alternate(a, b, x);
System.out.print("\nAfter exchange ");
System.out.print("\nx is : " + x);
}
}
// This code is contributed by 29AjayKumar
Python 3
# Python3 program to change value of x
# according to its current value.
# Function to alternate the values
def alternate(a, b, x):
x = a ^ b ^ x
print("After exchange")
print("x is", x)
# Driver code
a = -10
b = 15
x = a
print("x is", x)
alternate(a, b, x)
# This code is contributed
# by Shrikant13
C
// C# program to change value of x
// according to its current value.
using System;
public class GFG {
// Function to alternate the values
static int alternate(int a, int b, int x) {
return x = a ^ b ^ x;
}
// Main function
public static void Main() {
int a = -10;
int b = 15;
int x = a;
Console.Write("x is : " + x);
x = alternate(a, b, x);
Console.Write("\nAfter exchange ");
Console.Write("\nx is : " + x);
}
}
/*This code is contributed by Rajput-Ji*/
服务器端编程语言（Professional Hypertext Preprocessor 的缩写）
<?php
// PHP program to change value of x
// according to its current value.
// Function to alternate the values
function alternate(&$a, &$b, &$x)
{
$x = $a ^ $b ^ $x;
}
// Driver Code
$a = -10;
$b = 15;
$x = $a;
echo "x is : ", $x;
alternate($a, $b, $x);
echo "\nAfter exchange ";
echo "\nx is : ", $x;
// This code is contributed
// by akt_mit
?>
java 描述语言
<script>
// Javascript program to change value of x
// according to its current value.
// Function to alternate the values
function alternate(a , b , x) {
return x = a ^ b ^ x;
}
// Main function
var a = -10;
var b = 15;
var x = a;
document.write("x is : " + x);
x = alternate(a, b, x);
document.write("<br/>After exchange ");
document.write("<br/>x is : " + x);
// This code contributed by Rajput-Ji
</script>
Output:
x is : -10
After exchange
x is : 15
时间复杂度:该方法的时间复杂度为 O(1) T3】空间复杂度:该方法的空间复杂度为 O(1)
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