string removeKdigits(string num, int k) {

if(k <= 0) return num;

int n = num.length();

stack<int> indx;

indx.push(0);

int i = 1;

while(i < n and k > 0) {

if(indx.empty()) {

indx.push(i);

i++;

}

while(i < n and num[i] >= num[indx.top()]) {

indx.push(i);

i++;

}

num[indx.top()] = '#';

indx.pop();

k--;

}

while(k > 0) {

num[indx.top()] = '#';

indx.pop();

k--;

}

string result;

for(i = 0; i < n and !(num[i] > '0' and num[i] <= '9'); ++i);

for(; i < n; ++i) {

if(num[i] != '#') {

result += num[i];

}

}

if(result.empty()) result = "0";

return result;

}