Day 26 算法笔记之算法初步4.6 two pointers

目录

1.完美数列

2.Insert or Merge

3.median

4.find coins

---

1.完美数列

注意一下while循环里i和j的判断

#include <cstdio>
#include <cctype>
#include <cstring>
#include <math.h>
#include <iostream>
#include <algorithm>
#include <map>
using namespace std;

int main(){
	
	int n,m;
	scanf("%d %d",&n,&m);
	
	int martix[100];
	for(int i=0;i<n;i++){
		scanf("%d",&martix[i]);
	}
	
	sort(martix,martix+n);
	
	int i=0,j=0,counts=0;
	
	while(i<n&&j<n){
		while(j<n&&martix[j]<=martix[i]*m){
			counts = max(counts,j-i+1);
			j++;
		}
		i++;
	}
	
	printf("%d\n",counts);	
	return 0;
} 

2.Insert or Merge

精髓在插入排序和归并排序的细节处理上，节省了很多事

#include <cstdio>
#include <cctype>
#include <cstring>
#include <math.h>
#include <iostream>
#include <algorithm>
#include <map>
using namespace std;

const int N = 111;

int origin[N],tempori[N],changed[N];
int n;

bool issame(int a[],int b[]){
	for(int i=0;i<n;i++){
		if(a[i]!=b[i]){
			return false;
		}
	}
	return true;
}

bool showarray(int a[]){
	for(int i=0;i<n;i++){
		printf("%d",a[i]);
		if(i<n-1){
			printf(" ");
		}
	}
	printf("\n");
}

bool insertsort(){
	bool flag = false;
	
	for(int i=1;i<n;i++){
		if(i=1&&issame(tempori,changed)){
			flag= true;
	}
		
		int temp= tempori[i],j=i;
		while(j>0&&tempori[j-1]>temp){
			tempori[j] = tempori[j-1];
			j--;
		}
		tempori[j] = temp;
		if(flag==true){
			return true;
		}
	}
	return false;
	
}

void mergesort(){
	bool flag= false;
	for(int step=2;step/2<=n;step*=2){
		if(step!=2&&issame(tempori,changed)){
			flag= true;
		}
		
		for(int i=0;i<n;i+=step){
			sort(tempori+i,tempori+min(i+step,n));
		}
		
		if(flag==true){
			showarray(tempori);
			return;
		}
	}
}



int main(){
	
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		scanf("%d",&origin[i]);
		tempori[i] = origin[i];
	}
	
	for(int i=0;i<n;i++){
		scanf("%d",&changed[i]);
	}
	
	if(insertsort()){
		printf("Insertion Sort\n");
		showarray(tempori);
	}else{
		printf("Merge Sort\n");
		for(int i=0;i<n;i++){
			tempori[i] = origin[i];
		}
		mergesort();
	}
	
	return 0;
} 

3.median

细节也是满细节的

#include <cstdio>
#include <cctype>
#include <cstring>
#include <math.h>
#include <iostream>
#include <algorithm>
#include <map>
using namespace std;


int main(){
	
	int n,m;
	int a[100],b[100];
	
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		scanf("%d",&a[i]);
	}
	scanf("%d",&m);
	for(int j=0;j<m;j++){
		scanf("%d",&b[j]);
	}
	
	int i=0,j=0,count=(n+m-1)/2;
	while(count){
		if(a[i]<b[j]) i++;
		else j++;
		count--;
	}
	
	printf("%d %d\n",i,j);
	if(a[i]<b[j]){
		printf("%d\n",a[i]);
	}else{
		printf("%d\n",b[j]);
	}
	
	return 0;
} 

4.find coins

#include <cstdio>
#include <cctype>
#include <cstring>
#include <math.h>
#include <iostream>
#include <algorithm>
#include <map>
using namespace std;



int main(){
	
	int n,m;
	int martix[100];
	
	scanf("%d %d",&n,&m);
	for(int i=0;i<n;i++){
		scanf("%d",&martix[i]);
	}
	
	sort(martix,martix+n);
	
	int i=0,j=n-1,temp;
	while(i<j){
		temp = martix[i]+martix[j];
		if(temp==m){
			break;
		}else if(temp>m){
			j--;
		}else{
			i++;
		}
	}
	
	if(i==j){
		printf("NO Solution\n");
	}else{
		printf("%d %d\n",martix[i],martix[j]);
	}
	
	return 0;
}