SRandom API may return the same member of the set if input argument "count" is positive

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If k is set to zero,then the wile statement will be pass and idx_flag[0] will be set to 1;
If k is set to zero the second time, idx_flag[0] will be set to 2;
The first member of set will be return twice in the case above.
Further more , the biggest member will be returned with higher probability if the rand() function return the same value.
//......
int k = rand() % remain_card + 1;
int i = 0;
int cnt = 0; // the valid k-th number
while (i < card && cnt < k) {
if (idx_flag.find(i) == idx_flag.end()) {
cnt++;
}

            if (cnt == k) break;
            i++;
        }
        idx_flag[i]++;
        remain_card--;