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_465.java
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package com.fishercoder.solutions;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Stack;
/**
* 465. Optimal Account Balancing
*
* A group of friends went on holiday and sometimes lent each other money.
* For example, Alice paid for Bill's lunch for $10.
* Then later Chris gave Alice $5 for a taxi ride.
* We can model each transaction as a tuple (x, y, z) which means person x gave person y $z.
* Assuming Alice, Bill, and Chris are person 0, 1, and 2 respectively (0, 1, 2 are the person's ID),
* the transactions can be represented as [[0, 1, 10], [2, 0, 5]].
Given a list of transactions between a group of people, return the minimum number of transactions required to settle the debt.
Note:
A transaction will be given as a tuple (x, y, z). Note that x ? y and z > 0.
Person's IDs may not be linear, e.g. we could have the persons 0, 1, 2 or we could also have the persons 0, 2, 6.
Example 1:
Input:
[[0,1,10], [2,0,5]]
Output:
2
Explanation:
Person #0 gave person #1 $10.
Person #2 gave person #0 $5.
Two transactions are needed. One way to settle the debt is person #1 pays person #0 and #2 $5 each.
Example 2:
Input:
[[0,1,10], [1,0,1], [1,2,5], [2,0,5]]
Output:
1
Explanation:
Person #0 gave person #1 $10.
Person #1 gave person #0 $1.
Person #1 gave person #2 $5.
Person #2 gave person #0 $5.
Therefore, person #1 only need to give person #0 $4, and all debt is settled.
*/
public class _465 {
/**Reference: https://discuss.leetcode.com/topic/68948/easy-java-solution-with-explanation*/
public int minTransfers(int[][] transactions) {
if (transactions == null || transactions.length == 0) {
return 0;
}
Map<Integer, Integer> acc = new HashMap<>();
for (int i = 0; i < transactions.length; i++) {
int id1 = transactions[i][0];
int id2 = transactions[i][1];
int m = transactions[i][2];
acc.put(id1, acc.getOrDefault(id1, 0) - m);
acc.put(id2, acc.getOrDefault(id2, 0) + m);
}
List<Integer> negs = new ArrayList<>();
List<Integer> poss = new ArrayList<>();
for (Integer key : acc.keySet()) {
int m = acc.get(key);
if (m == 0) {
continue;
}
if (m < 0) {
negs.add(-m);
} else {
poss.add(m);
}
}
int ans = Integer.MAX_VALUE;
Stack<Integer> stNeg = new Stack<>();
Stack<Integer> stPos = new Stack<>();
for (int i = 0; i < 1000; i++) {
for (Integer num : negs) {
stNeg.push(num);
}
for (Integer num : poss) {
stPos.push(num);
}
int cur = 0;
while (!stNeg.isEmpty()) {
int n = stNeg.pop();
int p = stPos.pop();
cur++;
if (n == p) {
continue;
}
if (n > p) {
stNeg.push(n - p);
} else {
stPos.push(p - n);
}
}
ans = Math.min(ans, cur);
Collections.shuffle(negs);
Collections.shuffle(poss);
}
return ans;
}
}