牛客周赛 Round 29

题目

给定字符串s，字符串t，查找字符串s中包含字符串t中全部字符的最短子串

解题

通过滑动窗口来计算字符串s中包含字符串t的窗口，并按需调整窗口大小，取最小窗口大小返回

private static String findMinStringContainTarget(String source, String target) {
  if (StringUtils.isEmpty(source) || StringUtils.isEmpty(target) || source.length() < target.length()) {
    return "";
  }
  //记一下字符串t中每个字符及其数量
  Map<Character, Integer> targetCharCount = new HashMap<>();
  for (char item : target.toCharArray()) {
    Integer curCount = targetCharCount.getOrDefault(item, 0);
    targetCharCount.put(item, curCount + 1);
  }
  int sourceLength = source.length();
  int leftIndex = 0;
  int rightIndex = target.length() - 1;
  //记录最小覆盖字符串的两端下标
  int minLenLeftIndex = 0;
  int minLenRightIndex = sourceLength;
  boolean hasContain = false;
  while (rightIndex < sourceLength) {
    //记录下字符串s中在leftIndex到rightIndex之间的字符数
    Map<Character, Integer> rangeContains = new HashMap<>();
    for (int i = leftIndex; i <= rightIndex; i++) {
      Integer curCount = rangeContains.getOrDefault(source.charAt(i), 0);
      rangeContains.put(source.charAt(i), curCount + 1);
    }
    //判断子字符串中是否包含了字符串t中所有字符及其数量
    Iterator<Map.Entry<Character, Integer>> iterator = targetCharCount.entrySet().iterator();
    boolean contain = true;
    while (iterator.hasNext()) {
      Map.Entry<Character, Integer> next = iterator.next();
      if (!rangeContains.containsKey(next.getKey()) || rangeContains.get(next.getKey()) < next.getValue()) {
        contain = false;
        break;
      }
    }
    if (contain) {
      //当前子字符串包含了字符串t中的所有字符，则左边界右移
      if (minLenRightIndex - minLenLeftIndex > rightIndex - leftIndex) {
        minLenLeftIndex = leftIndex;
        minLenRightIndex = rightIndex;
        hasContain=true;
      }
      leftIndex++;
    } else {
      //当前子字符串不包含字符串t中的所有字符，则应该扩展子字符串，右边界右移
      rightIndex++;
      //右移时如果移动的字符不在字符串t的范围内，则继续右移
      while (rightIndex < sourceLength && !targetCharCount.containsKey(source.charAt(rightIndex))) {
        rightIndex++;
      }
    }
  }
  //表示两个字符串包含相同的字符
  if (hasContain&&minLenRightIndex == sourceLength) {
  return source.substring(minLenLeftIndex);
  }
  //表示字符串s不存在字符串包含字符串t
  if (minLenRightIndex == sourceLength) {
    return "";
  }
  return source.substring(minLenLeftIndex, minLenRightIndex + 1);
}