这道题是一道简单的dp题,就是求从第一个数到底行中的某个数的路径数字之和最大值。这道题的子问题就是求到每一行的每一个数的路径的最大数字和。
设:t[i][j]储存第i行第j列的数字。
maxsum[i][j]储存到第i行第j列数字的路径的最大数字和。
dp方程是:
maxsum[i][j] = (maxsum[i - 1][j - 1] + t[i][j]) > (maxsum[i - 1][j] + t[i][j]) ? (maxsum[i - 1][j - 1] + t[i][j])
: (maxsum[i - 1][j] + t[i][j]);
ps:这道题在poj上提交AC,但是在百练是提交内存溢出。
public class Main1163 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int[][] t = new int[n + 1][];
int[][] maxsum = new int[n + 1][];
for (int i = 1; i <= n; ++i) {
t[i] = new int[i+1];
maxsum[i] = new int[i+1];
for (int j = 1; j <= i; ++j) {
t[i][j] = sc.nextInt();
}
}
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= i; ++j) {
if (i - 1 == 0)
maxsum[1][1] = t[1][1];
else if (j - 1 == 0)
maxsum[i][j] = maxsum[i - 1][j] + t[i][j];
else if (j > i - 1)
maxsum[i][j] = maxsum[i - 1][j - 1] + t[i][j];
else {
maxsum[i][j] = (maxsum[i - 1][j - 1] + t[i][j]) > (maxsum[i - 1][j] + t[i][j]) ? (maxsum[i - 1][j - 1] + t[i][j])
: (maxsum[i - 1][j] + t[i][j]);
}
}
}
int max = -1;
for(int i = 1 ; i <= n ; ++i){
if(maxsum[n][i] > max)
max = maxsum[n][i];
}
System.out.println(max);
}
}