30 lines
599 B
Python
30 lines
599 B
Python
# RZ2T(SAM)_8.py
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import sys
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sys.stdin = open('input.txt', 'r')
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sys.stdout = open('output.txt', 'w')
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n = int(input())
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a = list(map(int, input().split()))
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counter_ros = 0
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counter_vio = 0
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ros = []
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vio = []
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for i in range(1, n+1):
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if a[i-1] == i % 2:
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if i % 2 == 0:
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ros.append(i-1)
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counter_ros += 1
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else:
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vio.append(i-1)
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counter_vio += 1
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if counter_vio == counter_ros:
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print(counter_ros)
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for i in range(counter_ros):
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print(ros[i]+1, ' ', vio[i]+1)
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else:
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print(-1)
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# ------------------------------------------ #
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