DFS to search all possible combine.

class Solution {    public int minTransfers(int[][] transactions) {        if (transactions.length == 0) return 0;        int nums = 0;        for (int[] trans : transactions) {            nums = Math.max(nums, Math.max(trans[0], trans[1]));        }        int[] debt = new int[nums + 1];        for (int[] trans : transactions) {            debt[trans[0]] += trans[2];            debt[trans[1]] -= trans[2];        }        return dfs(debt, 0, 0);    }        private int dfs(int[] debt, int index, int count) {        while (index < debt.length && debt[index] == 0) index++;        int result = Integer.MAX_VALUE;        for (int i = index + 1, prev = 0; i < debt.length; i++) {            if (debt[i] != prev && debt[i] * debt[index] < 0) {                debt[i] += debt[index];                result = Math.min(result, dfs(debt, index + 1, count + 1));                debt[i] -= debt[index];                prev = debt[i];            }        }        return result < Integer.MAX_VALUE ? result : count;    }}