【转】http://blog.csdn.net/zxy_snow/article/details/6005768
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#include <stdio.h>#include <stdlib.h>#include <iostream>#include <string.h>using namespace std;int sum,ways;int num[1010];int value,n;void DFS(int x){ if( sum == value ) { ways++; return ; } for(int i=x; i<=value; i++) { if( num[i] && sum + i <= value ) { num[i]--; sum += i; DFS(i); num[i]++; sum -= i; } }}int main(void){ int x,y; int pe = 0; while( cin >> value >> n ) { if( pe ) cout << endl; pe = 1; memset(num,0,sizeof(num)); sum = ways = 0; for(int i=0; i<n; i++) { cin >> x >> y; num[x] = y; } DFS(1); cout << ways << endl; }return 0;}?