60 lines
1.7 KiB
Python
60 lines
1.7 KiB
Python
#!/usr/bin/python
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# NOTE: THIS SOLUTION WORKS, BUT IT'S EXTREMELY SLOW. THE C VERSION RUNS IN A FEW SECONDS, THIS ONE TAKES SEVERAL MINUTES.
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#
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# NOTE: This problem is a more challenging version of Problem 81.
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#
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# The minimal path sum in the 5 by 5 matrix below, by starting in any cell in the left column and finishing in any cell in the right column,
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# and only moving up, down, and right, is indicated in red and bold; the sum is equal to 994.
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#
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# 131 673 *234* *103* *18*
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# *201* *96* *342* 965 150
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# 630 803 746 422 111
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# 537 699 497 121 956
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# 805 732 524 37 331
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#
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# Find the minimal path sum, in matrix.txt, a 31K text file containing a 80 by 80 matrix, from the left column to the right column.
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import sys
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from numpy import zeros
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from projecteuler import dijkstra, timing
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@timing
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def p082():
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try:
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with open('input/matrix.txt', 'r', encoding='utf-8') as fp:
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matrix = fp.readlines()
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except FileNotFoundError:
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print('Error while opening file matrix.txt')
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sys.exit(1)
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distances = zeros((80, 80), int)
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j = 0
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for i in matrix:
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matrix[j] = list(map(int, i.strip().split(',')))
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j = j + 1
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min_path = 999999999
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# Use Dijkstra's algorithm starting from all possible nodes in the first column.
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for i in range(80):
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dijkstra(matrix, distances, 80, 80, 1, 0, i)
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# For the current starting node, check if there is an ending node
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# with a smaller path cost than the current minimum.
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for j in range(80):
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if distances[j][79] < min_path:
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min_path = distances[j][79]
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print('Project Euler, Problem 82')
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print(f'Answer: {min_path}')
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if __name__ == '__main__':
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p082()
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