Create minimum-number-of-moves-to-make-palindrome.py

Author: kamyu104

Python/minimum-number-of-moves-to-make-palindrome.py

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+# Time:  O(nlogn)
+# Space: O(n)
+
+class BIT(object):  # 0-indexed
+    def __init__(self, n):
+        self.__bit = [0]*(n+1)
+
+    def add(self, i, val):
+        i += 1
+        while i < len(self.__bit):
+            self.__bit[i] += val
+            i += (i & -i)
+
+    def query(self, i):
+        i += 1
+        ret = 0
+        while i > 0:
+            ret += self.__bit[i]
+            i -= (i & -i)
+        return ret
+
+
+# greedy, bit, fenwick tree
+class Solution(object):
+    def minMovesToMakePalindrome(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        idxs = [[] for _ in xrange(26)]
+        for i, c in enumerate(s):
+            idxs[ord(c)-ord('a')].append(i)
+        targets, pairs = [0]*len(s), []
+        for c, idx in enumerate(idxs):
+            for i in xrange(len(idx)//2):
+                pairs.append((idx[i], idx[~i]))
+            if len(idx)%2:
+                targets[idx[len(idx)//2]] = len(s)//2
+        pairs.sort()
+        for i, (l, r) in enumerate(pairs):
+            targets[l], targets[r] = i, (len(s)-1)-i
+        bit = BIT(len(s))
+        result = 0
+        for i in targets:
+            result += i-bit.query(i-1)  # move from bit.query(i-1) to i
+            bit.add(i, 1)
+        return result
+
+
+# Time:  O(n^2)
+# Space: O(n)
+# greedy
+class Solution2(object):
+    def minMovesToMakePalindrome(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        s = list(s)
+        result = 0
+        while s:
+            i = s.index(s[-1])
+            if i == len(s)-1:
+                result += i//2
+            else:
+                result += i
+                s.pop(i)
+            s.pop()
+        return result