76 lines
1.7 KiB
C++
76 lines
1.7 KiB
C++
#include <array>
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#include <cstdint>
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#include <numeric>
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#include <vector>
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class Solution {
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using pad_t = std::array<int, 12>;
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static bool isValidMove(int i) {
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return i >= 0 && i < 12 && i != 9 && i != 11;
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}
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static int index(int x, int y) {
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if (x < 0 || x >= 3 || y < 0 || y >= 4) {
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return -1;
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}
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return y * 3 + x;
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}
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static int add(int x, int y) { return (x + y) % 1000000007; }
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static int get(const std::vector<pad_t>& dp, int it, int idx) {
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if (it < 0 || it >= static_cast<int>(dp.size())) {
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return 0;
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}
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if (!isValidMove(idx)) {
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return 0;
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}
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return dp[it][idx];
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}
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static void dpIteration(std::vector<pad_t>& dp, int it) {
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for (int i = 0; i < 12; ++i) {
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if (!isValidMove(i)) {
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continue;
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}
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int dx = -2, dy = -1;
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for (int j = 0; j < 8; ++j) {
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auto next = index(i % 3 + dx, i / 3 + dy);
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dp[it][i] = add(dp[it][i], get(dp, it - 1, next));
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// adjustment of the dx, dy
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dy *= -1;
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if (j % 2 == 1) {
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dx *= -1;
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}
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if (j % 4 == 3) {
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int d = dx;
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dx = dy;
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dy = d;
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}
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}
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}
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}
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public:
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int knightDialer(int n) {
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std::vector<pad_t> dp(n);
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dp[0].fill(1);
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dp[0][9] = 0;
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dp[0][11] = 0;
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for (int i = 1; i < n; ++i) {
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dpIteration(dp, i);
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}
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return std::accumulate(dp.back().begin(), dp.back().end(), 0, add);
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}
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};
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