POJ 2078

16ms 解法:

#include <cstdio>

//using namespace std;

int data[7][7];
int dp[7][7];
int row_min[7];
int row_max[7];

int n,min,max;

void solve(int row) {
    int i,j,pos,tmp, tmp_max;
    if (row == n) {
        max = dp[n-1][0];
        for (i = 0; i < n; i++) {
            if (max < dp[n-1][i]) {
                max = dp[n-1][i];
            }
        }
        if (min > max) {
            min = max;
        }
        return;
    }

    //prune, the above max value + current line min value > current answer min, then return
    if (row_max[row-1]+row_min[row]>min) {
        return;
    }

    for(i = 0; i < n; i++) {

        //tmp_max cal current row's dp max value
        tmp_max = -999999;

        for (j = 0; j < n; j++) {
            tmp = i+j;
            pos = tmp < n ? tmp : tmp-n;
            dp[row][pos] = dp[row-1][pos] + data[row][j];

            if (dp[row][pos] > tmp_max) {
                tmp_max = dp[row][pos];
            }
        }
        row_max[row] = tmp_max;

        solve(row+1);
    }

}

int main() {

    int i,j,val,mymin,mymax;

    while(scanf("%d", &n) && n != -1) {
    
        for (i = 0; i < n; i++) {
            mymin = 999999;
            for (j = 0; j < n; j++) {
                scanf("%d", &val);
                data[i][j] = val;
                if (val < mymin) {
                    mymin = val;
                }
            }
            row_min[i] = mymin; //cal min value for every row
        }

        mymax = -999999;
        for (i = 0; i < n; i++) {
            dp[0][i] = data[0][i];
            if (data[0][i] > mymax) {
                mymax = data[0][i];
            }
        }
        row_max[0] = mymax;  //first row's max value

        min = 9999999;
        solve(1);

        printf("%d
", min);

    }
    return 0;

}