此题解法：动态规划，倒骑毛驴。

在使用动态规划的时候，如果正着求难求，可以考虑倒着来。

这道题坑不少，自己代码能力太弱了，写代码的过程中总是容易犯细节错误。虽然大的方向是对的，但是小坑非常致命！

比如一开始下面这两句话写反了。

nowHeight = (int) Math.max(nowHeight, Math.ceil(h[i] * (M - y) * 1.0 / w[i])); y = 0;

import com.sun.rowset.internal.Row;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.util.Scanner;public class Main {int M, N;int w[], h[];Node f[][];class Node {    int rowHeight;//行高    int height;//高度    Node(int rowHeight, int height) {        this.rowHeight = rowHeight;        this.height = height;    }}void solve() {    int nowHeight = 0;//行高    int height = 0;//总高    int y = 0;//当前行位置    int ans = N * 107;    for (int i = 0; i < N - 1; i++) {        if (y == 0) {            ans = Math.min(ans, height + f[i + 1][0].height + f[i + 1][0].rowHeight);        } else {            ans = Math.min(ans, height + f[i + 1][y].height + Math.max(f[i + 1][y].rowHeight, nowHeight));        }        if (y + w[i] < M) {            y += w[i];            nowHeight = Math.max(nowHeight, h[i]);        } else if (y + w[i] == M) {            nowHeight = Math.max(h[i], nowHeight);            height += nowHeight;            nowHeight = 0;            y = 0;        } else {            nowHeight = (int) Math.max(nowHeight, Math.ceil(h[i] * (M - y) * 1.0 / w[i]));            height += nowHeight;            nowHeight = 0;            y = 0;        }    }    ans = Math.min(ans, height + nowHeight);    System.out.println(ans);}Main() throws FileNotFoundException {    Scanner cin = new Scanner(System.in);    // Scanner cin = new Scanner(new FileInputStream("in.txt"));    M = cin.nextInt();    N = cin.nextInt();    w = new int[N];    h = new int[N];    f = new Node[N + 1][M];    for (int i = 0; i < N; i++) {        w[i] = cin.nextInt();        h[i] = cin.nextInt();    }    cin.close();    for (int j = 0; j < M; j++) {        f[N][j] = new Node(0, 0);    }    for (int i = N - 1; i >= 0; i--) {        for (int j = 0; j < M; j++) {            if (j + w[i] < M) {                Node next = f[i + 1][j + w[i]];                f[i][j] = new Node(Math.max(h[i], next.rowHeight), next.height);            } else if (j + w[i] == M) {                Node next = f[i + 1][0];                f[i][j] = new Node(h[i], next.height + next.rowHeight);            } else {                int myh = (int) Math.ceil(h[i] * 1.0 * (M - j) / w[i]);                Node next = f[i + 1][0];                f[i][j] = new Node(myh, next.height + next.rowHeight);            }        }    }    solve();}public static void main(String[] args) throws FileNotFoundException {    new Main();}}