Tony's mouth is blowing (. Silanol) zzz

Depth-First Search

Start searching better from one side with fewer start states

Examples

Give you a pair of cards in the \ (n\) card, out of the next card needs to be the number of cards in front of the sum of the number of points, to find a legitimate solution

The forward search code for this topic is as follows:

void dfs(int depth, int sum){    if(depth == n){        output();        return ;        }    REP(i, 1, n){    if(!vis[i] && sum % a[i] == 0){        vis[i] = 1;        dfs(depth + 1, sum + a[i]);        vis[i] = 0;        }    }}

Obviously the initial branch is many, consider the reverse search

void dfs(int depth, int left){    if(depth == 0){output();return ;}    REP(i, 1, n){    if(!vis[i] && (left - a[i]) % a[i] == 0){        vis[i] = 1;        dfs(depth - 1, left - a[i]);        vis[i] = 0;        }    }}//调用dfs(n, sum[a[i]]);

Fewer initial branches, less search volume

Tony's mouth is blowing (. Silanol) zzz