POJ3740

一.  原题链接 http://poj.org/problem?id=3740

二.  思路：

1、直接DFS搜，然后记得把cin cout改成 scanf printf。就不会超时。这道题告诉我们分函数写的重要性。

2、跳舞链，多么优雅名字，写了好久的，然后为什么我写完之后，提交后的时间比DFS多呢。是我太弱了吧- -！

三. 代码

DFS 610ms

#include <iostream>#include <cstdio>#include <cstring>#include <queue>#include <algorithm>#include <vector>#include <string>using namespace std;int square[30][500], row, col, mark[500];int cntMark;int rememberJ[302];bool OK;bool checkRow(int i){    for(int j = 0; j < col; j++){        if(square[i][j] && mark[j])            return false;    }    return true;}//return the last index which is marked;int markRow(int i){    int j;    for(j = 0; j < col; j++){        if(square[i][j]){            cntMark++;            mark[j] = true;        }    }    return j - 1;}void disMark(int i, int j){    for(; j >= 0; j--){        if(square[i][j]){            cntMark--;            mark[j] = false;        }    }}void dfs(int i, int j){    if(col == cntMark){        OK = true;        return;    }    if(i == row || OK)        return ;   for(; i < row; i++){        if(checkRow(i)){            int preMark = markRow(i);            dfs(i + 1, preMark + 1);            disMark(i, preMark);        }   }}int main(){   // freopen("in.txt", "r", stdin);    int i, j;    while(scanf("%d%d", &row, &col) != EOF){        for(i = 0; i < row; i++)            for(j = 0; j < col; j++)            scanf("%d", &square[i][j]);        memset(mark, 0, sizeof(mark));        cntMark = 0;        OK = false;        dfs(0, 0);        if(OK)            printf("Yes, I found it\n");        else            printf("It is impossible\n");    }    return 0;}

跳舞链810ms

#include <iostream>#include <cstdio>#include <cstring>#include <queue>#include <algorithm>#include <vector>#include <string>using namespace std;const int m  = 18, n = 305;struct node{    node *l, *r, *u, *d;    int IdOfCol, IdOfRow;};node heap[m * n], *C[n], *head = NULL;int row, col, top;node *newNode(){    return &heap[top++];}void init(){    top = 0;    head = newNode();    int j;    for(j = 1; j <= col; j++){        C[j] = newNode();    }    for(j = 1; j <= col; j++){        C[j]->l = C[j-1];        C[j]->r = C[j+1];        C[j]->d = C[j]->u = C[j];        C[j]->IdOfCol = j;    }    head->IdOfCol = 0;    head->l = C[col];    head->r = C[1];    C[1]->l = head;    C[col]->r = head;}void del(node *C){    C->l->r = C->r;    C->r->l = C->l;    node *i, *j;    for(i = C->d; i != C; i = i->d){        for(j = i->r; j != i; j = j->r){            j->u->d = j->d;            j->d->u = j->u;        }    }}void resume(node *C){    C->l->r = C;    C->r->l = C;    node *i, *j;    for(i = C->d; i != C; i = i->d){        for(j = i->r; j != i; j = j->r){            j->u->d = j;            j->d->u = j;        }    }}bool dfs(){    node *cur = head->r, *i, *j;    if(cur == head)        return true;    for(i = cur->d; i != cur; i = i->d){        del(cur);        for(j = i->r; j != i; j = j->r){            del(C[j->IdOfCol]);        }        if(dfs())            return true;        resume(cur);        for(j = i->r; j != i; j = j->r){            resume(C[j->IdOfCol]);        }    }    return false;}int main(){    //freopen("in.txt", "r", stdin);    int i, j, buffer;    while(scanf("%d%d", &row, &col) != EOF){init();        for(i = 1; i <= row; i++){                node *p = NULL, *s = NULL;            for(j = 1; j <= col; j++){                scanf("%d", &buffer);                if(1 == buffer){                    p = newNode();                    if(!s)                       p->l = p->r = p;                    else                       p->l = s, p->r = s->r,                       s->r->l = p, s->r = p;                    s = p;                    p->d = C[j];p->u = C[j]->u;C[j]->u->d = p;C[j]->u = p;p->IdOfCol = j;p->IdOfRow = i;                }            }        }        if(dfs())            printf("Yes, I found it\n");        else            printf("It is impossible\n");    }    return 0;}