字符串匹配

//1.substring
class Solution {
    public int strStr(String haystack, String needle) {
        int h = haystack.length();
        int n = needle.length();
        for (int i = 0; i <= h - n; i++) {
            if (haystack.substring(i, i + n).equals(needle))
                return i;
        }
        return -1;
    }
}

//2.indexOf

public int strStr(String haystack, String needle) {
        return haystack.indexOf(needle);
 }

/**
　　indexOf源码：（找到首字母后双指针）

*/

//先在source中找到首字母与target相同的index。再用双指针判定，如果指到末尾则完全匹配，返回索引，
//否则回溯source下一个字符。（只保留重要部分）

static int indexOf(char[] source, int sourceOffset, int sourceCount,
            char[] target, int targetOffset, int targetCount,
            int fromIndex) {char first = target[targetOffset];
        int max = sourceOffset + (sourceCount - targetCount);

        for (int i = sourceOffset + fromIndex; i <= max; i++) {
            /* Look for first character. */
            if (source[i] != first) {
                while (++i <= max && source[i] != first);
            }

            /* Found first character, now look at the rest of v2 */
            if (i <= max) {
                int j = i + 1;
                int end = j + targetCount - 1;
                for (int k = targetOffset + 1; j < end && source[j]
                        == target[k]; j++, k++);

                if (j == end) {
                    /* Found whole string. */
                    return i - sourceOffset;
                }
            }
        }
        return -1;
    }