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34 lines
805 B
34 lines
805 B
/**
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* File: climbing_stairs_dfs_mem.dart
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* Created Time: 2023-08-11
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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/* 记忆化搜索 */
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int dfs(int i, List<int> mem) {
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// 已知 dp[1] 和 dp[2] ，返回之
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if (i == 1 || i == 2) return i;
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// 若存在记录 dp[i] ，则直接返回之
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if (mem[i] != -1) return mem[i];
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// dp[i] = dp[i-1] + dp[i-2]
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int count = dfs(i - 1, mem) + dfs(i - 2, mem);
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// 记录 dp[i]
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mem[i] = count;
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return count;
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}
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/* 爬楼梯：记忆化搜索 */
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int climbingStairsDFSMem(int n) {
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// mem[i] 记录爬到第 i 阶的方案总数，-1 代表无记录
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List<int> mem = List.filled(n + 1, -1);
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return dfs(n, mem);
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}
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/* Driver Code */
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void main() {
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int n = 9;
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int res = climbingStairsDFSMem(n);
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print("爬 $n 阶楼梯共有 $res 种方案");
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}
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