【Grind75Hard】1問目76. Minimum Window Substring

grind75_hard/01_76_Minimum Window Substring/level_1.py

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+# ポインタを2つ使い条件を満たす範囲を見つける。
+# まずtの文字全てが含まれるwindowを見つけるために、rightを進めていく
+# tの文字全てが含まれるwindowを見つけたら、leftを進めて無駄な文字を削除していく
+class Solution:
+    def minWindow(self, s: str, t: str) -> str:
+        t_count = defaultdict(int)
+        for c in t:
+            t_count[c] += 1
+        window_count = defaultdict(int)
+        left = 0
+        right = 0
+        match_num = 0
+        min_length = math.inf, None, None
+        while right < len(s):
+            if s[right] in t_count:
+                window_count[s[right]] += 1
+                if window_count[s[right]] == t_count[s[right]]:
+                    match_num += 1
+            while left <= right and match_num == len(t_count):
+                if min_length[0] > right - left:
+                    min_length = right - left, left, right
+                if s[left] in t_count:
+                    window_count[s[left]] -= 1
+                    if window_count[s[left]] < t_count[s[left]]:
+                        match_num -= 1
+                left += 1
+            right += 1
+        if min_length[0] == math.inf:
+            return ""
+        _, left, right = min_length
+        return s[left : right + 1]

grind75_hard/01_76_Minimum Window Substring/level_2.py

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+# rightをfor文で実装
+# 最小のwindowのindexのみを保持するように修正
+class Solution:
+    def minWindow(self, s: str, t: str) -> str:
+        t_count = defaultdict(int)
+        for c in t:
+            t_count[c] += 1
+        left = 0
+        match_num = 0
+        window_count = defaultdict(int)
+        min_window_index = (left, math.inf)
+        for right, c in enumerate(s):
+            if c not in t_count:
+                continue
+            window_count[c] += 1
+            if window_count[c] == t_count[c]:
+                match_num += 1
+            while left <= right and match_num == len(t_count):
+                if right - left + 1 < min_window_index[1] - min_window_index[0] + 1:
+                    min_window_index = (left, right)
+                if s[left] in t_count:
+                    window_count[s[left]] -= 1
+                    if window_count[s[left]] < t_count[s[left]]:
+                        match_num -= 1
+                left += 1
+        min_window_left, min_window_right = min_window_index
+        if min_window_right == math.inf:
+            return ""
+        return s[min_window_left : min_window_right + 1]

grind75_hard/01_76_Minimum Window Substring/level_3.py

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+class Solution:
+    def minWindow(self, s: str, t: str) -> str:
+        t_count = defaultdict(int)
+        for c in t:
+            t_count[c] += 1
+        left = 0
+        min_window_index = (left, math.inf)
+        window_count = defaultdict(int)
+        match_num = 0
+        for right, c in enumerate(s):
+            if c not in t_count:
+                continue
+            window_count[c] += 1
+            if window_count[c] == t_count[c]:
+                match_num += 1
+            while left <= right and match_num == len(t_count):
+                if right - left + 1 < min_window_index[1] - min_window_index[0] + 1:
+                    min_window_index = (left, right)
+                if s[left] in t_count:
+                    window_count[s[left]] -= 1
+                    if window_count[s[left]] < t_count[s[left]]:
+                        match_num -= 1
+                left += 1
+        left, right = min_window_index
+        if right == math.inf:
+            return ""
+        return s[left : right + 1]

grind75_hard/01_76_Minimum Window Substring/level_4.py

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+# 変数名の修正
+# defaultdectを[0]*128に変更
+# tに含まれていない文字もカウントするように修正
+class Solution:
+    def minWindow(self, s: str, t: str) -> str:
+        num_chars_in_t = [0] * 128
+        for c in t:
+            num_chars_in_t[ord(c)] += 1
+        num_needed_matches = 128 - num_chars_in_t.count(0)
+        left = 0
+        num_matches = 0
+        num_chars_in_window = [0] * 128
+        min_window_index = (left, len(s))
+        for right, c in enumerate(s):
+            num_chars_in_window[ord(c)] += 1
+            if num_chars_in_window[ord(c)] == num_chars_in_t[ord(c)]:
+                num_matches += 1
+            while left <= right and num_matches == num_needed_matches:
+                if right - left + 1 < min_window_index[1] - min_window_index[0] + 1:
+                    min_window_index = (left, right)
+                num_chars_in_window[ord(s[left])] -= 1
+                if num_chars_in_window[ord(s[left])] < num_chars_in_t[ord(s[left])]:
+                    num_matches -= 1
+                left += 1
+        min_window_left, min_window_right = min_window_index
+        if min_window_right == len(s):
+            return ""
+        return s[min_window_left : min_window_right + 1]