UVa 116 - Unidirectional TSP（DP）

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单向TSP。

从后往前依次dp左，左上，左下。然后记录当前对应的最小字典序。

#include <iostream>#include <algorithm>#include <cstring>using namespace std;const int INF = 1 << 27;const int maxn = 123;int ans, first;int a[maxn][maxn], d[maxn][maxn], Next[maxn][maxn];int main() {    int m, n;    while(cin >> m >> n) {        memset(a, 0, sizeof(a));        memset(d, 0, sizeof(d));        memset(Next, 0, sizeof(Next));        ans = INF;        for(int i = 0; i < m; i++) {            for(int j = 0; j < n; j++) {                cin >> a[i][j];            }        }        for(int j = n - 1; j >= 0; j--) {            for(int i = 0; i < m; i++) {                if(j == n - 1) {                    d[i][j] = a[i][j];                } else {                    int row[] = {i, i - 1, i + 1};                    if(i == 0) row[1] = m - 1;                    if(i == m - 1) row[2] = 0;                    sort(row, row + 3);                    d[i][j] = INF;                    for(int k = 0; k < 3; k++) {                        int t = d[row[k]][j + 1] + a[i][j];                        if(t < d[i][j]) {                            d[i][j] = t;                            Next[i][j] = row[k];                        }                    }                }                if(j == 0) {                    if(d[i][j] < ans) {                        ans = d[i][j];                        first = i;                    }                }            }        }//        cout << first << endl;        for(int j = 0, i = first; j < n; i = Next[i][j], j++) {            if(j) cout << " ";            cout << i + 1;        }        cout << endl << ans << endl;    }    return 0;}

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