Codeforce#479Div3第一场

A. Wrong Subtraction

输入两个数，n和k，n是初始的数，k为操作数，如果个位为就除以10，不为0则减1，求k次操作后的数

#include<cstdio>


using namespace std;

int main() {
    int n, k;
    scanf("%d%d", &n, &k);
    while (k--) {
        if (n % 10 == 0)
            n /= 10;
        else
            n--;
    }
    printf("%d\n", n);
    return 0;
}

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B. Two-gram

输入一个数n，再输入一个长度为n的字符串

#include<cstdio>


using namespace std;
char s[150];
int a[150];
int main() {
    int n;
    scanf("%d", &n);
    scanf("%s", s);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++)
            if (s[i] == s[j] && s[i + 1] == s[j + 1])
                a[i]++;
    }
    int Max = -1;
    int m = 0;
    for (int i = 0; i < n; i++)
        if (a[i] > Max)
            Max = a[i] , m = i;
    printf("%c%c\n", s[m], s[m + 1]);
    return 0;
}

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C. Less or Equal

输入n和k，n个数，求x，使x为n个数中小于等于x的数的个数为k

#include<cstdio>
#include<algorithm>
 
using namespace std;
int a[200050];
int main() {
    int n, k;
    scanf("%d%d", &n, &k);
    for (int i = 0; i < n; i++)    scanf("%d", &a[i]);
    sort(a, a + n);
    if (k == 0) {
        if (a[0] == 1)    printf("-1\n");
        else
        {
            printf("1\n");
            return 0;
        }
    }
    else {
        if (a[k] == a[k - 1])    printf("-1\n");
        else
        {
            printf("%d\n", a[k - 1]);
        }
    }
    return 0;
}

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D. Divide by three, multiply by two

输出一组数进行排序，排序方法为前面的数为后面的数的3倍或一半

#include<cstdio>
#include<iostream>


using namespace std;

const int maxn = 10;
int n;
bool vis[maxn];
int ans[maxn];

void DFS(int step) {
    if (step >= n) {
        for (int i = 0; i < n; i++)
            cout << ans[i] << " ";
        cout << endl;
        return;
    }
    for (int i = 1; i <= n; i++) {
        if (!vis[i]) {
            vis[i] = true;
            ans[step] = i;
            DFS(step + 1);
            vis[i] = false;
        }
    }
}

int main() {
    cin >> n;
    DFS(0);
    return 0;
}

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先写这么多，赶火车，有时间再写