在合并排序C ++中使用合并时的随机值

``````void merge(int a[], int left_low,  int left_high, int right_low, int right_high)
``````

``````a = {1, 3,     10 ,         4,    7,      8}
^         ^            ^             ^
left_low  left_high    right_low     right_high
``````

``````void merge(int a[], int left_low,  int left_high,
int right_low, int right_high) {
int temp[right_high + 1]; // temporary array to store the result
int left_i = left_low, right_i = right_low, temp_i = 0;

// while the temporary array is not filled
while(temp_i != right_high + 1)
{
if(left_i == left_high + 1)
temp[temp_i++] = a[right_i++];
else if(right_i == right_high + 1)
temp[temp_i++] = a[left_i++];
else if(a[left_i] < a[right_i])
temp[temp_i++] = a[left_i++];
else
temp[temp_i++] = a[right_i++];
} // end while
for(int i = 0; i < temp_i; ++i)
a[i] = temp[i];
}
``````

``````template<class T>
void print (std::string label, T a[], int length, bool report_sorted) {
bool sorted = true;
std::cout << label;
for (int i=0; i<length; ++i) {
std::cout << a[i];
if (i == length-1)
std::cout << std::endl;
else {
std::cout << ", ";
if (a[i] > a[i+1])
sorted = false;
}
}
if (report_sorted)
std::cout << (sorted ? "    Sorted" : "    Not Sorted") << std::endl;
}

void shuffle(int values[], int length) {
std::vector<int> v_values;
for (int i=0; i<length; ++i)
v_values.push_back(values[i]);
std::random_shuffle(v_values.begin(),v_values.end());
for (int i=0; i<length; ++i)
values[i] = v_values[i];
}

//Recursive Merge Sort
template<class T>
void merge_sort(T a[], int low, int high) {
if (high - low < 1)               //Base case: 0 or 1 value to sort -> sorted
return;
else {
int mid = (low + high)/2;       //Split in 1/2
merge_sort(a, low, mid);        //Recursively sort low to mid
merge_sort(a, mid+1, high);     //Recursively sort mid+1 to high
merge(a, low,mid, mid+1,high);  //Merge sorted parts of array
}
}

//Standard Merge Sort (calls a generalized one, with more parameters)
template<class T>
void merge_sort(T a[], int length) {
merge_sort(a, 0, length-1);
}

std::cout << "\n\nTesting merge in merge sort" << std::endl;
int test_merge_sort[10] = {1,2,3,4,5,6,7,8,9,10};
for (int i=0; i<5; i++) {
shuffle(test_merge_sort, 10);
print("\n  Array before sort: ", test_merge_sort, 10, false);
merge_sort(test_merge_sort, 10);
print("  Array after  sort: ", test_merge_sort, 10, true);
}
``````

`````` Array before sort: 3, 9, 2, 5, 8, 4, 6, 10, 1, 7
Array after  sort: -944749486, 4, 5439488, 0, 5443192, 5443196, 1975317641, -944749486, 4, 1995111146
Not Sorted

Array before sort: 1995111146, 1975317641, 4, 0, -944749486, 5443192, 5443196, 5439488, 4, -944749486
Array after  sort: -944749486, 4, 5439488, 0, 5443192, 5443196, 1975317641, -944749486, 4, 1995111146
Not Sorted

Array before sort: -944749486, -944749486, 5443196, 4, 5439488, 1995111146, 5443192, 1975317641, 0, 4
Array after  sort: -944749486, 4, 5439488, 0, 5443192, 5443196, 1975317641, -944749486, 4, 1995111146
Not Sorted

Array before sort: 1975317641, -944749486, 4, 4, 5439488, 5443192, 5443196, -944749486, 0, 1995111146
Array after  sort: -944749486, 4, 5439488, 0, 5443192, 5443196, 1975317641, -944749486, 4, 1995111146
Not Sorted

Array before sort: -944749486, 5443192, 5443196, 1975317641, 4, 0, -944749486, 5439488, 1995111146, 4
Array after  sort: -944749486, 4, 5439488, 0, 5443192, 5443196, 1975317641, -944749486, 4, 1995111146
Not Sorted
``````

`left_low`为零时，这没有区别，因此您的测试用例运行良好。但是一旦`left_low`变为非零值（例如，当对数组的右半部分进行排序时），您的代码就会“超调”两个数组，将垃圾值放入`tmp`数组`a`中并在其中覆盖值

``````for(int i = 0; i < temp_i; ++i)
a[i+left_low] = temp[i];
``````

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