计蒜客蓝桥杯模拟赛5 最大组合数

#include <stdio.h>
long long max(long long x, long long y) {
    return x > y ? x : y;
}
long long test(int a[], int n) {
    long long ret = 0;
    for (int i = 0; i < n; ++i) {
        int tp = a[i];
        int j = 1;
        //计算位数 
        while(tp) {
            j *= 10;
            tp /= 10;
        }
        ret = ret * j + a[i];
    }
    return ret;
}

long long f(int a[], int k) {
    if (k == 6) {
        return test(a, k);
    }
    long long ret = 0;
    for(int i = k; i < 6; ++i) {
        int t = a[k];
        a[k] = a[i];
        a[i] = t;
        ret = max(ret, f(a,k+1));//看到k==6,就知道此处用递归
        t = a[k];
        a[k] = a[i];
        a[i] = t;
    }
    return ret;
}

int main() {
    int a[6] = {517, 283, 429, 65, 6566, 32};
    printf("%lld\n", f(a, 0));
    return 0;
}