[LeetCode] Sliding Windows

最新推荐文章于 2025-12-21 14:33:21 发布

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本文详细介绍滑动窗口算法的基本原理及其在不同场景中的应用。包括如何创建窗口、调整窗口大小来更新匹配结果，适用于寻找最长或最短子串、子数组等问题。文章还提供了实现模板，并讨论了算法的时间复杂度。

1. Algorithmn Analysis

1.1 Implementation Template

1.2 Usual question variation

1.3 Complexity

2. Sliding Windows Optimization

3. Suitable Questions

3.1 substring without repeating characters

3.2 substring match

3.3 subarray

1. Algorithm Analysis

Create a window [left, right)
Increasing right edge to expand the window and update the matching results
if the window big enough, increasing left edge to shrink the window and update the result
Repeat step 2 and 3, until right edge reach end of input

1.1 Implementation Template

vector<int> letter(128,0);
for(auto c:target) {
    letter[c]++;
}

int l = 0, r = 0;
int matched = 0;
while(r < input.size()) {
    char c = input[r++]; //expend the window
    if(letter[c] > 0)
        matched++;
    letter[c]--; // non target char will be negative
    
    if(r-l == target.size()) { //condition to shrink the window
        if(matched == target.size())
            ans.push_back();
        //shrink window
        if(letter[input[l++]++ > 0)
            matched--;
    }
}

return and;