コード
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;
public class Main {
private static class Task {
void solve(FastScanner in, PrintWriter out) {
int N = in.nextInt();
int M = in.nextInt();
ArrayList<Edge>[] graph = new ArrayList[M + 1];
for (int i = 0; i < M + 1; i++) graph[i] = new ArrayList<>();
for (int i = 0; i < N; i++) {
int S = in.nextInt();
int L = in.nextInt();
graph[S].add(new Edge(S + L, 0));
}
for (int i = 0; i < M; i++) {
graph[i].add(new Edge(i + 1, 1));
graph[i + 1].add(new Edge(i, 1));
}
PriorityQueue<Edge> queue = new PriorityQueue<>();
int[] dist = new int[M + 1];
Arrays.fill(dist, Integer.MAX_VALUE / 2);
dist[0] = 0;
queue.add(new Edge(0, 0));
while (!queue.isEmpty()) {
Edge p = queue.poll();
for (Edge e : graph[p.to]) {
if (dist[e.to] > p.cost + e.cost) {
dist[e.to] = p.cost + e.cost;
queue.add(new Edge(e.to, dist[e.to]));
}
}
}
out.println(M - dist[M]);
}
class Edge implements Comparable<Edge> {
int to, cost;
Edge(int to, int cost) {
this.to = to;
this.cost = cost;
}
@Override
public int compareTo(Edge o) {
return this.cost - o.cost;
}
}
}
public static void main(String[] args) {
OutputStream outputStream = System.out;
FastScanner in = new FastScanner();
PrintWriter out = new PrintWriter(outputStream);
Task solver = new Task();
solver.solve(in, out);
out.close();
}
private static class FastScanner {
private final InputStream in = System.in;
private final byte[] buffer = new byte[1024];
private int ptr = 0;
private int bufferLength = 0;
private boolean hasNextByte() {
if (ptr < bufferLength) {
return true;
} else {
ptr = 0;
try {
bufferLength = in.read(buffer);
} catch (IOException e) {
e.printStackTrace();
}
if (bufferLength <= 0) {
return false;
}
}
return true;
}
private int readByte() {
if (hasNextByte()) return buffer[ptr++];
else return -1;
}
private static boolean isPrintableChar(int c) {
return 33 <= c && c <= 126;
}
private void skipUnprintable() {
while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;
}
boolean hasNext() {
skipUnprintable();
return hasNextByte();
}
public String next() {
if (!hasNext()) throw new NoSuchElementException();
StringBuilder sb = new StringBuilder();
int b = readByte();
while (isPrintableChar(b)) {
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
long nextLong() {
if (!hasNext()) throw new NoSuchElementException();
long n = 0;
boolean minus = false;
int b = readByte();
if (b == '-') {
minus = true;
b = readByte();
}
if (b < '0' || '9' < b) {
throw new NumberFormatException();
}
while (true) {
if ('0' <= b && b <= '9') {
n *= 10;
n += b - '0';
} else if (b == -1 || !isPrintableChar(b)) {
return minus ? -n : n;
} else {
throw new NumberFormatException();
}
b = readByte();
}
}
double nextDouble() {
return Double.parseDouble(next());
}
double[] nextDoubleArray(int n) {
double[] array = new double[n];
for (int i = 0; i < n; i++) {
array[i] = nextDouble();
}
return array;
}
double[][] nextDoubleMap(int n, int m) {
double[][] map = new double[n][];
for (int i = 0; i < n; i++) {
map[i] = nextDoubleArray(m);
}
return map;
}
public int nextInt() {
return (int) nextLong();
}
public int[] nextIntArray(int n) {
int[] array = new int[n];
for (int i = 0; i < n; i++) {
array[i] = nextInt();
}
return array;
}
}
}