LEETCODE ALGORITHM:1208. Get Equal Substrings Within Budget

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题目

You are given two strings s and t of the same length. You want to change s to t. Changing the i-th character of s to i-th character of t costs |s[i] - t[i]| that is, the absolute difference between the ASCII values of the characters.

You are also given an integer maxCost.

Return the maximum length of a substring of s that can be changed to be the same as the corresponding substring of twith a cost less than or equal to maxCost.

If there is no substring from s that can be changed to its corresponding substring from t, return 0.

Example 1:

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Input: s = "abcd", t = "bcdf", maxCost = 3
Output: 3
Explanation: "abc" of s can change to "bcd". That costs 3, so the maximum length is 3.

Example 2:

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Input: s = "abcd", t = "cdef", maxCost = 3
Output: 1
Explanation: Each character in s costs 2 to change to charactor in t, so the maximum length is 1.

Example 3:

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Input: s = "abcd", t = "acde", maxCost = 0
Output: 1
Explanation: You can't make any change, so the maximum length is 1.

Constraints:

  • 1 <= s.length, t.length <= 10^5
  • 0 <= maxCost <= 10^6
  • s and t only contain lower case English letters.

题解

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//滑动窗口法，纯暴力法最后一组数据会超时
class Solution {
public:
    int equalSubstring(string s, string t, int maxCost) {
        int ans=0;
        vector<int> diff(s.length());
        for(int i=0;i<t.length();i++)
        {
            diff[i]=abs(t[i]-s[i]);
        }
        int j=0,k=0,tmpcost=0;
        while(j<s.length())
        {
            while(k<s.length()&&tmpcost+diff[k]<=maxCost)
            {
                tmpcost+=diff[k];
                k++;
            }
            ans=max(ans,k-j);
            j++;
            tmpcost-=diff[j-1];
            if(s.length()-j<ans) break;
        }
        return ans;
    }
};