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#include <iostream>
#include <cstring>
using namespace std;
int dp[1001][1001], a[1001][1001];
int main()
{
int m, n;
memset(dp, 0x3f, sizeof(dp));
memset(a, 0x3f, sizeof(a));
cin >> n;
for (int i = 1; i <= n; i++)
{
for (int j = 1; j <= i; j++)
{
cin >> a[i][j];
}
}
dp[n][1] = a[n][1];
for (int i = n; i >= 1; i--)
{
dp[i][1] = min(dp[i][1], dp[i][i] + a[i][1]); //末到当前行首
dp[i][1] = min(dp[i][1], dp[i + 1][i + 1] + a[i][1]); //还能这么跑？！下一层最后一个（逆序dp
for (int j = 1; j <= i; j++)
{
dp[i][j] = min(dp[i][j], dp[i][j - 1] + a[i][j]); //左边的
dp[i][j] = min(dp[i][j], min(dp[i + 1][j], dp[i + 1][j + 1]) + a[i][j]); //下边+右下
}
dp[i][i] = min(dp[i][i], dp[i][1] + a[i][i]); //最后到第一个
dp[i][i] = min(dp[i][i], dp[i + 1][1] + a[i][i]); //最后到下一行第一个
for (int j = i - 1; j >= 1; --j)
dp[i][j] = min(dp[i][j], dp[i][j + 1] + a[i][j]); //从右往左跑右边的
//第二次dp
dp[i][1] = min(dp[i][1], dp[i][i] + a[i][1]); //到行首
dp[i][1] = min(dp[i][1], dp[i + 1][i + 1] + a[i][1]);
for (int j = 1; j <= i; j++)
{
dp[i][j] = min(dp[i][j], dp[i][j - 1] + a[i][j]);
dp[i][j] = min(dp[i][j], min(dp[i + 1][j], dp[i + 1][j + 1]) + a[i][j]);
}
dp[i][i] = min(dp[i][i], dp[i][1] + a[i][i]);
dp[i][i] = min(dp[i][i], dp[i + 1][1] + a[i][i]);
}
cout << dp[1][1] << endl;
return 0;
}
/*看了题解 */
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