1048. Find Coins (25)

Eva loves to collect coins from all over the universe, including some other planets like Mars. One day she visited a universal shopping mall which could accept all kinds of coins as payments. However, there was a special requirement of the payment: for each bill, she could only use exactly two coins to pay the exact amount. Since she has as many as 10⁵ coins with her, she definitely needs your help. You are supposed to tell her, for any given amount of money, whether or not she can find two coins to pay for it.

Input Specification:

Each input file contains one test case. For each case, the first line contains 2 positive numbers: N (<=10⁵, the total number of coins) and M(<=10³, the amount of money Eva has to pay). The second line contains N face values of the coins, which are all positive numbers no more than 500. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print in one line the two face values V₁ and V₂ (separated by a space) such that V₁ + V₂ = M and V₁ <= V₂. If such a solution is not unique, output the one with the smallest V₁. If there is no solution, output "No Solution" instead.

Sample Input 1:

8 15
1 2 8 7 2 4 11 15

Sample Output 1:

4 11

Sample Input 2:

7 14
1 8 7 2 4 11 15

Sample Output 2:

No Solution

#include<cstdio>
const int maxn = 100010;
int hashTable[maxn] = {0};
int main(){
    int n,m;
    scanf("%d%d",&n,&m);
    int coin;
    for(int i = 0; i < n; i++){
        scanf("%d",&coin);
        hashTable[coin]++;
    }
    for(int i = 1; i <= m; i++){
    if(hashTable[i] && hashTable[m - i]){
        if(i == m - i && hashTable[i] <= 1){
            continue;
        }
        printf("%d %d",i,m - i);
        return 0;
       }
    }
    printf("No Solution");
    return 0;
}

//二分法
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn = 100010;
int A[maxn];

int Bin(int left,int right,int key){
    int mid;
    while(left <= right){
        mid = (left+right)/2;
        if(A[mid] > key) right = mid - 1;
        else if(A[mid] < key) left = mid + 1;
        else return mid;
    }
    return -1;
}

int main(){
    int n,m,i;
    scanf("%d%d",&n,&m);
    for(i = 0 ; i < n; i++){
        scanf("%d",&A[i]);
    }
    sort(A,A+n);
    for(i = 0 ; i < n; i++){
        int pos = Bin(0,n-1,m-A[i]);
        if(pos != -1 && pos != i){
            printf("%d %d",A[i],A[pos]);
            return 0;
        }
    }
    if(i == n) printf("No Solution");
    return 0;
}

//twopointer 
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn = 100010;
int a[maxn];

void twopointer(int n,int m){
    int i = 0, j = n-1;
    while(i < j){
        if(a[i]+a[j] == m) break;
        else if(a[i]+a[j] > m) j--;
        else i++;
    }
    if(i < j) printf("%d %d",a[i],a[j]);
    else printf("No Solution");
}

int main(){
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i = 0 ; i < n ; i++){
        scanf("%d",&a[i]);
    }
    sort(a,a+n);
    twopointer(n,m);
    return 0;
}