ts-ds-tool/src/algorithms/kmp/kmp.ts

Data structure and algorithm of TypeScript

function getNext(word: string){
    const next = [0];
    let wordIndex = 1;
    let prevIndex = 0;
    while (wordIndex < word.length) {
        if (word[prevIndex] === word[wordIndex]) {
            next[wordIndex] = prevIndex + 1;
            prevIndex ++;
            wordIndex ++;
        }else if (prevIndex === 0) {
            next[wordIndex] = 0;
            wordIndex ++;
        }else {
            // 当前没有，从当前的公共前缀中寻找
            prevIndex = next[prevIndex - 1];
        }
    }
    return next;
}
/**
 * kmp算法（根据字串前后缀相同而比较）
 * @param text
 * @param word
 */
export function kmp(text: string , word: string){
    if (text === null || text === undefined){
        return -1;
    }
    if (word === null || word === undefined){
        return -1;
    }
    if (word.length === 0){
        return 0;
    }
    const next: Array<number> = getNext(word);
    let wordIndex = 0;
    let textIndex = 0;
    while (textIndex < text.length) {
        if (text[textIndex] === word[wordIndex]){
            if (wordIndex === word.length - 1){
                return textIndex - wordIndex;
            }
            textIndex ++;
            wordIndex ++;
        }else if (wordIndex > 0) {
            wordIndex = next[wordIndex - 1];
        }else {
            wordIndex = 0;
            textIndex ++;
        }
    }
    return -1;
}