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Optimal Account Balancing in C++
Suppose a group of friends went on holiday and sometimes they lent each other money. So as an example, Amit paid for Bikram's lunch for $10. Then later Chandan gave Amit $5 for a taxi fare. We have to design a model where each transaction is taken as a tuple (x, y, z) which means person x gave person y $z.
Assuming Amit, Bikram, and Chandan are person 0, 1, and 2 respectively the transactions can be represented as [[0, 1, 10], [2, 0, 5]]. If we have a list of transactions between a group of people, we have to find the minimum number of transactions required to settle the debt.
So, if the input is like [[0,1,10], [2,0,5]], then the output will be 2, as person #0 gave person #1 $10. Then person #2 gave person #0 $5. Here two transactions are needed. One way to settle the debt is person #1 pays person #0 and #2 $5 each.
To solve this, we will follow these steps −
Define an array v
Define a function dfs(), this will take idx,
ret := inf
while (idx < size of v and not v[idx] is non-zero), do −
(increase idx by 1)
for initialize i := idx + 1, when i − size of v, update (increase i by 1), do −
if v[i] * v[idx] < 0, then −
v[i] := v[i] + v[idx]
ret := minimum of ret and 1 + dfs(idx + 1)
v[i] := v[i] - v[idx]
return (if ret is same as inf, then 0, otherwise ret)
From the main method do the following −
Define one map m
n := size of t
for initialize i := 0, when i < n, update (increase i by 1), do −
u := t[i, 0], v := t[i, 1]
bal := t[i, 2]
m[u] := m[u] + bal
m[v] := m[v] - bal
for each key-value pair i in m, do −
if value of i, then −
insert value of i at the end of v
(increase i by 1)
return minimum of dfs(0) and size of v
Example
Let us see the following implementation to get better understanding −
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
vector<int> v;
int dfs(int idx) {
int ret = INT_MAX;
while (idx < v.size() && !v[idx])
idx++;
for (int i = idx + 1; i < v.size(); i++) {
if (v[i] * v[idx] < 0) {
v[i] += v[idx];
ret = min(ret, 1 + dfs(idx + 1));
v[i] -= v[idx];
}
}
return ret == INT_MAX ? 0 : ret;
}
int minTransfers(vector<vector<int>>&t) {
map<int, int> m;
int n = t.size();
for (int i = 0; i < n; i++) {
int u = t[i][0];
int v = t[i][1];
int bal = t[i][2];
m[u] += bal;
m[v] -= bal;
}
map<int, int>::iterator i = m.begin();
while (i != m.end()) {
if (i->second)
v.push_back(i->second);
i++;
}
return min(dfs(0), (int)v.size());
}
};
main() {
Solution ob;
vector<vector<int>> v = {{0,1,10},{2,0,5}};
cout << (ob.minTransfers(v));
}Input
{{0,1,10},{2,0,5}}Output
2
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