前端-KMP匹配

/**
 * [indexing description]: 求模式串viceStr字符串在主串manStr中的位置
 * @param  {[type]} mainStr [主串]
 * @param  {[type]} viceStr [模式串]
 * @return {[type]}         [返回模式串在主串中的位置]
 */
function indexing(mainStr, viceStr) {
  let i = 0, j = 0, mainLen = mainStr.length, viceLen = viceStr.length;
  while (i < mainLen && j < viceLen) {
    if (mainStr[i] === viceStr[j]) {
      ++i;
      ++j;
    } else {
      i = i - j + 1;
      j = 0;
    }
  }
  if (j >= viceLen) {
    return i - viceLen;
  } else return -1;
}

const a = 'ababcabcacbab';
const b = 'abcac';
const index = indexing(a, b);
console.log('the position in mainStr is: ', index)
console.log(a.indexOf(b))

const c = 'cacbabc'
const indexC = indexing(a, c);
console.log('the position in mainStr is: ', indexC)
console.log(a.indexOf(c))