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;
}