ajout TD4

Algo_ex3.c

@@ -0,0 +1,78 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static size_t ipow(size_t a, unsigned b) { 
+    size_t r = 1; while (b--) r *= a; return r;
+}
+
+static int cmp_int(const void *a, const void *b) { 
+    int ia = *(const int*)a, ib = *(const int*)b;
+    return (ia > ib) - (ia < ib);
+}
+
+
+static void reorder_blocks(int *base, size_t block_sz, size_t M,const size_t *idx)
+{
+    size_t group_sz = block_sz * M;
+    int *tmp = malloc(group_sz * sizeof(int));
+    for (size_t j = 0; j < M; ++j)
+        memcpy(tmp + j*block_sz, base + idx[j]*block_sz, block_sz*sizeof(int));
+    memcpy(base, tmp, group_sz * sizeof(int));
+    free(tmp);
+}
+
+
+void sort_ND(int *a, unsigned N, size_t M)
+{
+    const size_t total = ipow(M, N);
+
+
+    for (size_t off = 0; off < total; off += M)
+        qsort(a + off, M, sizeof(int), cmp_int);
+
+    for (unsigned level = 2; level <= N; ++level) {
+        size_t block_sz = ipow(M, level - 1);
+        size_t group_sz = block_sz * M;
+        size_t groups   = total / group_sz;
+
+        long *sums = malloc(M * sizeof(long));
+        size_t *idx = malloc(M * sizeof(size_t));
+
+        for (size_t g = 0; g < groups; ++g) {
+            int *base = a + g * group_sz;
+
+
+            for (size_t j = 0; j < M; ++j) {
+                long s = 0;
+                int *p = base + j * block_sz;
+                for (size_t t = 0; t < block_sz; ++t) s += p[t];
+                sums[j] = s;
+                idx[j] = j;
+            }
+
+            for (size_t i = 0; i + 1 < M; ++i)
+                for (size_t j = i + 1; j < M; ++j)
+                    if (sums[idx[j]] < sums[idx[i]]) {
+                        size_t tmp = idx[i]; idx[i] = idx[j]; idx[j] = tmp;
+                    }
+
+
+            reorder_blocks(base, block_sz, M, idx);
+        }
+        free(sums); free(idx);
+    }
+}
+
+
+int main(void) {
+    size_t M = 3; unsigned N = 2;
+    int a[] = { 0,3,2,  9,4,5,  4,1,3 };
+    sort_ND(a, N, M);
+
+    for (size_t i = 0; i < M; ++i) {
+        for (size_t j = 0; j < M; ++j) printf("%d ", a[i*M + j]);
+        printf("\n");
+    }
+    return 0;
+}