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Commit 8fea23e

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solves knight probability in java
1 parent cb82764 commit 8fea23e

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-30
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2 files changed

+29
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β€ŽREADME.md

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Original file line numberDiff line numberDiff line change
@@ -362,6 +362,7 @@
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| 682 | [Baseball Game](https://leetcode.com/problems/baseball-game) | [![Java](assets/java.png)](src/BaseballGame.java) [![Python](assets/python.png)](python/baseball_game.py) | |
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| 686 | [Repeated String Match](https://leetcode.com/problems/repeated-string-match) | | |
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| 687 | [Longest Univalue Path](https://leetcode.com/problems/longest-univalue-path) | | |
365+
| 688 | [Knight Probability in Chessboard](https://leetcode.com/problems/knight-probability-in-chessboard) | [![Java](assets/java.png)](src/KnightProbabilityInChessboard.java) | |
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| 690 | [Employee Importance](https://leetcode.com/problems/employee-importance) | | |
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| 693 | [Binary Number with Alternating Bits](https://leetcode.com/problems/binary-number-with-alternating-bits) | [![Java](assets/java.png)](src/BinaryNumberWithAlternatingBits.java) [![Python](assets/python.png)](python/binary_number_with_alternating_bits.py) | |
367368
| 696 | [Count Binary Substrings](https://leetcode.com/problems/count-binary-substrings) | [![Java](assets/java.png)](src/CountBinarySubstrings.java) [![Python](assets/python.png)](python/count_binary_substrings.py) | |

β€Žsrc/KnightProbabilityInChessboard.java

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
1+
// https://leetcode.com/problems/knight-probability-in-chessboard
2+
// T: O(n^2 * k)
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// S: O(n^2)
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15
import java.util.ArrayList;
26
import java.util.HashMap;
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import java.util.List;
@@ -13,7 +17,6 @@ static class Position {
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this.n = n;
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this.row = row;
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this.column = column;
16-
1720
}
1821

1922
private void normalize() {
@@ -28,7 +31,7 @@ private void normalize() {
2831

2932
private int normalize(int index) {
3033
if (index >= (n + 1) / 2) {
31-
return n - index;
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return n - index - 1;
3235
}
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return index;
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}
@@ -46,13 +49,6 @@ private Position apply(Movement movement) {
4649
};
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}
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49-
private boolean isValid() {
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return row >= 0
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&& row < n
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&& column >= 0
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&& column < n;
54-
}
55-
5652
@Override
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public boolean equals(Object o) {
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if (this == o) return true;
@@ -65,14 +61,6 @@ public boolean equals(Object o) {
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public int hashCode() {
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return 31 * row + column;
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}
68-
69-
@Override
70-
public String toString() {
71-
return "Position{" +
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"row=" + row +
73-
", column=" + column +
74-
'}';
75-
}
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}
7765

7866
private record State(int n, int k, Position position) { }
@@ -88,17 +76,16 @@ private enum Movement {
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LEFT_BOTTOM
8977
}
9078

91-
private final Map<Position, List<Movement>> allowedMovements = new HashMap<>();
92-
private final Map<State, Double> results = new HashMap<>();
79+
private static final Map<Position, List<Movement>> allowedMovements = new HashMap<>();
80+
private static final Map<State, Double> results = new HashMap<>();
81+
private static int[][] validMoves;
9382

94-
public double knightProbability(int n, int k, int row, int column) {
83+
public staticdouble knightProbability(int n, int k, int row, int column) {
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computeValidMovements(n);
96-
System.out.println(allowedMovements);
9785
return getKnightProbability(n, k, new Position(row, column, n));
9886
}
9987

100-
private double getKnightProbability(int n, int k, Position position) {
101-
if (!position.isValid()) return 0;
88+
private static double getKnightProbability(int n, int k, Position position) {
10289
if (k == 0) return 1;
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10491
position.normalize();
@@ -111,26 +98,37 @@ private double getKnightProbability(int n, int k, Position position) {
11198
return answer;
11299
}
113100

114-
int sumOfProbabilities = 0;
101+
double sumOfProbabilities = 0;
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for (Movement movement : allowedMovements.get(position)) {
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Position newPosition = position.apply(movement);
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sumOfProbabilities += getKnightProbability(n, k - 1, newPosition);
118105
}
119-
double answer = ((double) sumOfProbabilities) / 8;
106+
double answer = sumOfProbabilities / 8;
120107
results.put(state, answer);
121108
return answer;
122109
}
123110

124-
private void computeValidMovements(int n) {
111+
private staticvoid computeValidMovements(int n) {
125112
for (int row = 0 ; row < (n + 1) / 2 ; row++) {
126113
for (int column = row ; column < (n + 1) / 2 ; column++) {
127114
Position position = new Position(row, column, n);
128115
allowedMovements.put(position, knightMovementsAt(position));
129116
}
130117
}
118+
fillValidMovesTable(n);
119+
}
120+
121+
private static void fillValidMovesTable(int n) {
122+
final int length = (n + 1) / 2;
123+
validMoves = new int[length][length];
124+
for (int row = 0 ; row < length ; row++) {
125+
for (int column = row ; column < length ; column++) {
126+
validMoves[row][column] = allowedMovements.get(new Position(row, column, n)).size();
127+
}
128+
}
131129
}
132130

133-
private List<Movement> knightMovementsAt(Position position) {
131+
private staticList<Movement> knightMovementsAt(Position position) {
134132
final List<Movement> movements = new ArrayList<>();
135133
if (isValidIndices(position.row - 2, position.column - 1, position.n)) movements.add(Movement.TOP_LEFT);
136134
if (isValidIndices(position.row - 2, position.column + 1, position.n)) movements.add(Movement.TOP_RIGHT);
@@ -143,14 +141,14 @@ private List<Movement> knightMovementsAt(Position position) {
143141
return movements;
144142
}
145143

146-
private boolean isValidIndices(int row, int column, int n) {
144+
private staticboolean isValidIndices(int row, int column, int n) {
147145
return row >= 0
148146
&& row < n
149147
&& column >= 0
150148
&& column < n;
151149
}
152150

153-
private int validMoves(Position position) {
154-
return allowedMovements.get(position).size();
151+
private staticint validMoves(Position position) {
152+
return validMoves[position.row][position.column];
155153
}
156154
}

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