README_EN.md

1208. Get Equal Substrings Within Budget

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Description

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:

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:

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:

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.

Solutions

Python3

class Solution:
    def equalSubstring(self, s: str, t: str, maxCost: int) -> int:
        n = len(s)
        presum = [0] * (n + 1)
        for i in range(n):
            presum[i + 1] = presum[i] + abs(ord(s[i]) - ord(t[i]))
        left, right = 0, n

        def check(l):
            i = 0
            while i + l - 1 < n:
                j = i + l - 1
                if presum[j + 1] - presum[i] <= maxCost:
                    return True
                i += 1
            return False

        while left < right:
            mid = (left + right + 1) >> 1
            if check(mid):
                left = mid
            else:
                right = mid - 1
        return left

Java

class Solution {
    public int equalSubstring(String s, String t, int maxCost) {
        int n = s.length();
        int[] presum = new int[n + 1];
        for (int i = 0; i < n; ++i) {
            presum[i + 1] = presum[i] + Math.abs(s.charAt(i) - t.charAt(i));
        }
        int left = 0, right = n;
        while (left < right) {
            int mid = (left + right + 1) >>> 1;
            if (check(mid, presum, maxCost, n)) {
                left = mid;
            } else {
                right = mid - 1;
            }
        }
        return left;
    }

    private boolean check(int l, int[] s, int maxCost, int n) {
        int i = 0;
        while (i + l - 1 < n) {
            int j = i + l - 1;
            if (s[j + 1] - s[i] <= maxCost) {
                return true;
            }
            ++i;
        }
        return false;
    }
}

C++

class Solution {
public:
    int equalSubstring(string s, string t, int maxCost) {
        int n = s.size();
        vector<int> presum(n + 1);
        for (int i = 0; i < n; ++i) presum[i + 1] = presum[i] + abs(s[i] - t[i]);
        int left = 0, right = n;
        while (left < right)
        {
            int mid = left + right + 1 >> 1;
            if (check(mid, presum, maxCost, n)) left = mid;
            else right = mid - 1;
        }
        return left;
    }

    bool check(int l, vector<int>& s, int maxCost, int n) {
        int i = 0;
        while (i + l - 1 < n)
        {
            int j = i + l - 1;
            if (s[j + 1] - s[i] <= maxCost) return true;
            ++i;
        }
        return false;
    }
};

Go

func equalSubstring(s string, t string, maxCost int) int {
	n := len(s)
	presum := make([]int, n+1)
	for i, c := range s {
		presum[i+1] = presum[i] + abs(int(c)-int(t[i]))
	}

	left, right := 0, n
	check := func(l int) bool {
		i := 0
		for i+l-1 < n {
			j := i + l - 1
			if presum[j+1]-presum[i] <= maxCost {
				return true
			}
			i++
		}
		return false
	}
	for left < right {
		mid := (left + right + 1) >> 1
		if check(mid) {
			left = mid
		} else {
			right = mid - 1
		}
	}
	return left
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

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