21. 1~n任意取数组成m

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输入两个整数n 和m，从数列1，2，3.......n 中随意取几个数,

使其和等于m ,要求将其中所有的可能组合列出来.

HANDWRITING:

void search(int n, int m, int *com, int pos) {if (m == 0) {for (int i = pos - 1; i >= 0; --i) cout<<com[i]<<" ";cout<<endl;}int s = m < n ? m : n;while (s > 0) {com[pos] = s;search(s - 1, m - s, com, pos + 1);--s;}}void combination (int n, int m) {int *com = new int[n];search(n, m, com, 0);delete [] com;}

ANSWER FROM:http://blog.csdn.net/v_july_v/article/details/6870251
This is a combination generation problem.

void findCombination(int n, int m) {  if (n>m) findCombination(m, m);  int aux[n];  memset(aux, 0, n*sizeof(int));  helper(m, 0, aux);}void helper(int dest, int idx, int aux[], int n) {  if (dest == 0)     dump(aux, n);  if (dest <= 0 || idx==n) return;  helper(dest, idx+1, aux, n);  aux[idx] = 1;  helper(dest-idx-1, idx+1, aux, n);  aux[idx] = 0;}void dump(int aux[], int n) {  for (int i=0; i<n; i++)     if (aux[i]) printf(“%3d”, i+1);  printf(“\n”);}

PS: this is not an elegant implementation, however, it is not necessary to use gray code or other techniques for such a problem, right?