LeetCode 119. Pascal's Triangle II

这个问题最开始可以像前面一个题一样，用多个数组，然后取那一行
我开始只想用一个ret数组，发现总是出错，后面用tmp数组，可以了

int* getRow(int rowIndex, int* returnSize) {
    int *ret = (int*)malloc(sizeof(int) * (rowIndex+1));
    int *tmp = (int*)malloc(sizeof(int) * (rowIndex+1));
    ret[0] = 1;
    *returnSize = rowIndex + 1;
    if (rowIndex == 0) {
        return ret;
    }
    ret[1] = 1;
    if(rowIndex == 1) {
        return ret;
    }
    for (int i = 2; i <= rowIndex; ++i) {
        tmp[0]=1;
        tmp[i] = 1;
        for (int j = 0; j < i-1; ++j) {
            tmp[j+1] = ret[j] + ret[j+1];
        }
        for (int j = 0; j <= i; ++j) {
            ret[j]=tmp[j];
        }
    }
    free(tmp);
    return ret;
}

现在内存55%，有点多
在讨论中翻到这个：https://leetcode.com/problems/pascals-triangle-ii/discuss/38575/Share-my-c-code-easy-understand
发现居然可以倒着算，这样就不用tmp数组了

int* getRow(int rowIndex, int* returnSize) {
    int *ret = (int*)malloc(sizeof(int) * (rowIndex+1));
    ret[0] = 1;
    *returnSize = rowIndex + 1;
    if (rowIndex == 0) {
        return ret;
    }
    ret[1] = 1;
    if(rowIndex == 1) {
        return ret;
    }
    for (int i = 2; i <= rowIndex; ++i) {
        ret[0]=1;
        ret[i] = 1;
        for (int j = i-1; j > 0; --j) {
            ret[j] = ret[j] + ret[j-1];
        }
    }
    return ret;
}

内存变成65%，还有进步空间

int* getRow(int rowIndex, int* returnSize) {
    int *ret = (int*)malloc(sizeof(int) * (rowIndex+1));
    *returnSize = rowIndex + 1;
    for (int i = 0; i < *returnSize; ++i) {
        ret[i]=1;
    }
    if (rowIndex == 0) {
        return ret;
    }
    if(rowIndex == 1) {
        return ret;
    }
    for (int i = 2; i <= rowIndex; ++i) {
        for (int j = i-1; j > 0; --j) {
            ret[j] = ret[j] + ret[j-1];
        }
    }
    return ret;
}

把初始化放在一起，变成85%
还有没有办法变成90+？