HDU 4857/bestcoder round#1 1001 (Reverse build)

This problem needs careful analysis of the topic, otherwise test instructions easy to understand the error, should pay attention to the following situation

As far as possible, the smallest row of the front, and then the small as far as possible to the front, and then go on

Such as

Input

1

3 1

3 1

Output

3 1 2

Analysis: We should let 1 as far as possible in front, and then as far as possible to make 2 rows of the front ... So the result of 2 3 1 is wrong

Idea: Topology sequencing (reverse build + queue)//To solve the above example, if we are to build a map, each time the selection of the minimum number of zero output can not meet the above case;

If we try to reverse-build, each time we choose the maximum number output of zero in degrees is just the reverse of the correct result (the inverse of the province and check set, the training of reverse thinking)

#include <vector> #include <queue> #include <cstdio> #include <cstring> #include <stack>    using namespace Std;const int max=30010;vector<int> g[max];struct node{int x; int y;}    Wd[100010];struct cmp1{bool Operator () (int &a,int &b) {return a<b;    }};p riority_queue<int,vector<int>,cmp1>pq1;int ind[max];int n,m;stack<int> st;int main () {int T;    scanf ("%d", &t);        while (t--) {scanf ("%d%d", &n,&m);        for (int i=1;i<=n;++i) g[i].clear ();        memset (IND,0,SIZEOF (Ind));        int x, y;            for (int i=1;i<=m;++i) {scanf ("%d%d", &x,&y);            G[y].push_back (x);        ind[x]++;        } while (!pq1.empty ()) Pq1.pop ();        for (int i=1;i<=n;++i) {if (ind[i]==0) Pq1.push (i);        } while (!st.empty ()) St.pop ();        int tmp;    while (!pq1.empty ()) {tmp=pq1.top ();        Pq1.pop ();            St.push (TMP);            int len=g[tmp].size ();                for (int i=0;i<len;++i) {ind[g[tmp][i]]--;            if (ind[g[tmp][i]]==0) Pq1.push (G[tmp][i]);        }} tmp=st.top ();        St.pop ();            while (!st.empty ()) {printf ("%d", TMP);            Tmp=st.top ();        St.pop ();    } printf ("%d\n", TMP); } return 0;}

Harvesting: The training of Reverse thinking (reverse mapping, reverse processing, etc.)

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HDU 4857/bestcoder round#1 1001 (Reverse build)