[LintCode] Nuts and Bolts

The question is actually a quick sort problem. The basic idea is:

1st, we pick a “nut” from nuts pile.

2nd we divide bolts into two parts according to the “nut”;

3rd we find the matching bolt

4th then we divide our nuts into two parts

5th using recursion to sort our bolts and nuts!

Done.

How to partition? it takes some time to figure it out…qwq

/**
* class Comparator {
*     public:
*      int cmp(string a, string b);
* };
* You can use compare.cmp(a, b) to compare nuts "a" and bolts "b",
* if "a" is bigger than "b", it will return 1, else if they are equal,
* it will return 0, else if "a" is smaller than "b", it will return -1.
* When "a" is not a nut or "b" is not a bolt, it will return 2, which is not valid.
*/
class Solution {
public:
/**
* @param nuts: a vector of integers
* @param bolts: a vector of integers
* @param compare: a instance of Comparator
* @return: nothing
*/
void sortNutsAndBolts(vector<string> &nuts, vector<string> &bolts, Comparator compare) {
// write your code here
if(nuts.empty() || bolts.empty()) return;
int n = nuts.size(), m = bolts.size();
if(m!=n) return;
quickSort(nuts,bolts,compare, 0, n-1);
}
void quickSort(vector<string>& nuts, vector<string>& bolts, Comparator compare, int start, int end){
if(start >= end) return;
int idx = partition(nuts,bolts[start], compare, start, end);
partition(bolts, nuts[idx], compare, start, end);

quickSort(nuts, bolts, compare, start, idx-1);
quickSort(nuts, bolts, compare, idx+1, end);
}
int partition(vector<string>& NorB, string pivot, Comparator compare, int start, int end){
int m = start;// m indicates the actual position of pivot.
for(int i = start+1; i<=end; ++i){
if(compare.cmp(pivot, NorB[i]) == 1 || compare.cmp(NorB[i],pivot) == -1){
swap(NorB[++m],NorB[i]);
}else if(compare.cmp(pivot,NorB[i]) == 0 || compare.cmp(NorB[i], pivot) == 0){
swap(NorB[start],NorB[i]);
--i;
}
}
swap(NorB[m], NorB[start]);
return m;
}
};