leetcode/322.coin-change.java at main · jameszhan02/leetcode · GitHub

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/*
 * @lc app=leetcode id=322 lang=java
 *
 * [322] Coin Change
 */

// @lc code=start
class Solution {
  public int coinChange(int[] coins, int amount) {
        if (amount == 0) return 0;

        // BFS用队列
        Queue<Integer> queue = new LinkedList<>();
        boolean[] visited = new boolean[amount + 1];

        queue.offer(amount);
        int steps = 0;

        while (!queue.isEmpty()) {
            steps++; // 进入新一层
            int size = queue.size(); // 当前层有多少个节点

            for (int i = 0; i < size; i++) {
                int curr = queue.poll();

                // 试每一种硬币
                for (int coin : coins) {
                    int next = curr - coin;

                    if (next == 0) return steps;
                    if (next < 0) continue;
                    if (visited[next]) continue;

                    visited[next] = true;
                    queue.offer(next);
                }
            }
        }

        return -1; // 凑不出来
    }
}
// @lc code=end