【POJ1077】Eight【IDA*】

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【题目链接】

学习一发IDA*。

/* Pigonometry */#include <cstdio>#include <iostream>using namespace std;const int maxn = 4, maxm = 105, inf = 0x3f3f3f3f;char opt[] = {'u', 'd', 'l', 'r'};int dx[] = {-1, 1, 0, 0};int dy[] = {0, 0, -1, 1};int mp[maxn][maxn], ed[maxn][maxn];bool found;char solu[maxm];inline int read() {char ch = getchar(); for(; !(ch == 'x' || (ch >= '0' && ch <= '9')); ch = getchar());return ch == 'x' ? 0 : ch - '0';}inline int intabs(int x) {return x < 0 ? -x : x;}inline int getH() {int res = 0;for(int i = 1; i <= 3; i++) for(int j = 1; j <= 3; j++) if(mp[i][j]) {int x = (mp[i][j] - 1) / 3 + 1, y = (mp[i][j] - 1) % 3 + 1;res += intabs(i - x) + intabs(j - y);}return res;}inline int dfs(int x, int y, int d, int lim) {int h = getH();if(h == 0 || found) {found = 1;return d;}if(d + h > lim) return d + h;int nowlim = inf;for(int i = 0; i < 4; i++) {int xx = x + dx[i], yy = y + dy[i];if(xx < 1 || xx > 3 || yy < 1 || yy > 3) continue;swap(mp[x][y], mp[xx][yy]);solu[d] = opt[i];int nextlim = dfs(xx, yy, d + 1, lim);nowlim = min(nowlim, nextlim);if(found) return nowlim;swap(mp[x][y], mp[xx][yy]);}return nowlim;}int main() {int sx, sy;for(int i = 1; i <= 3; i++) for(int j = 1; j <= 3; j++) {mp[i][j] = read();if(!mp[i][j]) sx = i, sy = j;ed[i][j] = (i - 1) * 3 + j;}ed[3][3] = 0;found = 0;int deplim = getH();while(deplim < 100 && !found) deplim = dfs(sx, sy, 0, deplim);if(!found) printf("unsolvable\n");else {solu[deplim] = '\0';printf("%s", solu);}return 0;}

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