Language: C

#include <stdio.h>
#include <string.h>

#define SENTINEL 1000000000

void mergeSort(int A[],int left,int right){
  int i,mid;
  if(left+1<right){
    mid=(left+right)/2;
    mergeSort(A,left,mid);
    mergeSort(A,mid,right);
    merge(A,left,mid,right);
  }
}



void merge(int A[],int left,int mid,int right){
  int n1,n2,i,j,k;
  int *L,*R;
  n1=mid-left;
  n2=right-mid;
  L=(int *)malloc(sizeof(int)*(n1+1));
  R=(int *)malloc(sizeof(int)*(n2+1));
  for(i=0;i<=n1-1;i++){
    L[i]=A[left+i];
  }
  for(j=0;j<=n2-1;j++){
    R[j]=A[mid+j];
  }
  L[n1]=SENTINEL;
  R[n2]=SENTINEL;
  i=0;
  j=0;
  for(k=left;k<=right-1;k++){
   if(L[i]<=R[j]){
      A[k]=L[i];
      i++;
      count++;
    }
    else{
      A[k]=R[j];
      j++;
      count++;
    }
  }
  free(L);
  free(R);
}

int main(){
  int n,h,i,j,s,ans=0,ruiseki=0,tmp,max=0;
  scanf("%d %d",&n,&h);
  int a[n],b[n];
  for(i=0;i<=n-1;i++){
    scanf("%d %d",&a[i],&b[i]);
  }
  for(i=0;i<=n-1;i++){
    if(max <= a[i]){
      max = a[i];
    }
  }
  mergeSort(B,0,n-1)
  for(i=0;i<n;i++){
    if(max < b[i]){
      ruiseki += b[i];
      ans += 1;
      if(ruiseki >= h){
        break;
      }
    }else{
      break;
    }
  }
  if(ruiseki < h){
    s = h-ruiseki;
    if(s%max == 0){
      ans += s/max;
    }else{
      ans += s/max + 1;
    }
  }
  printf("%d",ans);
  return 0;
}

Compiler output:
main.c: In function 'mergeSort':
main.c:12:5: error: implicit declaration of function 'merge' [-Wimplicit-function-declaration]
   12 |     merge(A,left,mid,right);
      |     ^~~~~
main.c: At top level:
main.c:18:6: warning: conflicting types for 'merge'; have 'void(int *, int,  int,  int)'
   18 | void merge(int A[],int left,int mid,int right){
      |      ^~~~~
main.c:12:5: note: previous implicit declaration of 'merge' with type 'void(int *, int,  int,  int)'
   12 |     merge(A,left,mid,right);
      |     ^~~~~
main.c: In function 'merge':
main.c:23:12: error: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
   23 |   L=(int *)malloc(sizeof(int)*(n1+1));
      |            ^~~~~~
main.c:3:1: note: include '<stdlib.h>' or provide a declaration of 'malloc'
    2 | #include <string.h>
  +++ |+#include <stdlib.h>
    3 | 
main.c:23:12: warning: incompatible implicit declaration of built-in function 'malloc' [-Wbuiltin-declaration-mismatch]
   23 |   L=(int *)malloc(sizeof(int)*(n1+1));
      |            ^~~~~~
main.c:23:12: note: include '<stdlib.h>' or provide a declaration of 'malloc'
main.c:39:7: error: 'count' undeclared (first use in this function)
   39 |       count++;
      |       ^~~~~
main.c:39:7: note: each undeclared identifier is reported only once for each function it appears in
main.c:47:3: error: implicit declaration of function 'free' [-Wimplicit-function-declaration]
   47 |   free(L);
      |   ^~~~
main.c:47:3: note: include '<stdlib.h>' or provide a declaration of 'free'
main.c:47:3: warning: incompatible implicit declaration of built-in function 'free' [-Wbuiltin-declaration-mismatch]
main.c:47:3: note: include '<stdlib.h>' or provide a declaration of 'free'
main.c: In function 'main':
main.c:63:13: error: 'B' undeclared (first use in this function)
   63 |   mergeSort(B,0,n-1)
      |             ^
main.c:63:21: error: expected ';' before 'for'
   63 |   mergeSort(B,0,n-1)
      |                     ^
      |                     ;
   64 |   for(i=0;i<n;i++){
      |   ~~~