回答編集履歴
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コードの追加
test
CHANGED
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@@ -23,3 +23,107 @@
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再帰呼出しで、ローカルに大きな配列を確保し続けると、
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スタックオーバーフローが起きやすくなりますよ。
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### 追記
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最初に1回 msort の中で必要な領域を確保しておけば、
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再帰呼出しの merge_sort ではそれを使うだけのコードを書いてみました。
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```C
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#include <stdio.h> // printf, putchar
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#include <stdlib.h> // malloc, free
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#define N 8
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void show(int x[], int n)
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{
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for (int i = 0; i < n; i++) printf(" %d", x[i]);
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putchar('\n');
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}
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void merge(int x[], int m, int y[], int n, int t[])
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{
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int i = 0, j = 0, k = 0;
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while (j < m && k < n) t[i++] = (x[j] < y[k]) ? x[j++] : y[k++];
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while (j < m) t[i++] = x[j++];
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while (k < n) t[i++] = y[k++];
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}
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void merge_sort(int x[], int n, int t[])
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{
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if (n < 2) return;
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int n1 = n / 2, n2 = n - n1;
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merge_sort(x, n1, t);
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merge_sort(x + n1, n2, t);
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merge(x, n1, x + n1, n2, t);
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for (int i = 0; i < n; i++) x[i] = t[i];
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}
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void msort(int x[], int n, int y[])
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{
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int *t = malloc(sizeof(int) * n * 2);
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if (!t) { puts("out of memory"); return; }
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for (int i = 0; i < n; i++) t[i] = x[i];
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merge_sort(t, n, t + n);
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for (int i = 0; i < n; i++) y[i] = t[i];
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free(t);
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}
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int main()
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{
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int x[N] = { 18, 37, 21, 14, 7, 12, 19, 6 }, y[N];
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show(x, N);
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msort(x, N, y);
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show(y, N);
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}
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```
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