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package class19;
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public class Code03_HorseJump {
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public static int ways(int a, int b, int step) {
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return f(0, 0, step, a, b);
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}
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public static int f(int i, int j, int step, int a, int b) {
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if (i < 0 || i > 9 || j < 0 || j > 8) {
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return 0;
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}
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if (step == 0) {
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return (i == a && j == b) ? 1 : 0;
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}
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return f(i - 2, j + 1, step - 1, a, b)
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+ f(i - 1, j + 2, step - 1, a, b)
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+ f(i + 1, j + 2, step - 1, a, b)
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+ f(i + 2, j + 1, step - 1, a, b)
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+ f(i + 2, j - 1, step - 1, a, b)
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+ f(i + 1, j - 2, step - 1, a, b)
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+ f(i - 1, j - 2, step - 1, a, b)
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+ f(i - 2, j - 1, step - 1, a, b);
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}
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public static int waysdp(int a, int b, int s) {
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int[][][] dp = new int[10][9][s+1];
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dp[a][b][0] = 1;
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for(int step = 1 ; step <= s;step++ ) { // 按层来
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for(int i = 0 ; i < 10;i++) {
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for(int j = 0 ; j < 9; j++) {
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dp[i][j][step] = getValue(dp,i - 2, j + 1, step - 1)
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+ getValue(dp,i - 1, j + 2, step - 1)
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+ getValue(dp,i + 1, j + 2, step - 1)
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+ getValue(dp,i + 2, j + 1, step - 1)
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+ getValue(dp,i + 2, j - 1, step - 1)
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+ getValue(dp,i + 1, j - 2, step - 1)
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+ getValue(dp,i - 1, j - 2, step - 1)
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+ getValue(dp,i - 2, j - 1, step - 1);
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}
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}
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}
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return dp[0][0][s];
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}
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// 在dp表中，得到dp[i][j][step]的值，但如果(i，j)位置越界的话，返回0；
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public static int getValue(int[][][] dp, int i, int j, int step) {
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if (i < 0 || i > 9 || j < 0 || j > 8) {
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return 0;
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}
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return dp[i][j][step];
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}
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public static void main(String[] args) {
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int x = 7;
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int y = 7;
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int step = 10;
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System.out.println(ways(x, y, step));
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System.out.println(waysdp(x, y, step));
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}
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}
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