add new solutions

solutions/12/q1292/solution.go

@@ -0,0 +1,51 @@
+package q1292
+
+func pfSum(mat [][]int) [][]int {
+	w, h := len(mat[0])+1, len(mat)+1
+	pfs := make([][]int, h)
+	for i := range pfs {
+		pfs[i] = make([]int, w)
+	}
+
+	for y := 1; y < h; y++ {
+		for x := 1; x < w; x++ {
+			pfs[y][x] = mat[y-1][x-1] + pfs[y][x-1] + pfs[y-1][x] - pfs[y-1][x-1]
+		}
+	}
+	return pfs
+}
+
+func sumOfSquare(pfs [][]int, x, y, w int) int {
+	return pfs[y+w][x+w] - pfs[y][x+w] - pfs[y+w][x] + pfs[y][x]
+}
+
+func hasSquare(pfs [][]int, edgeLen, threshold int) bool {
+	w, h := len(pfs[0])-1, len(pfs)-1
+	for y := range h - edgeLen + 1 {
+		for x := range w - edgeLen + 1 {
+			if sumOfSquare(pfs, x, y, edgeLen) <= threshold {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func maxSideLength(mat [][]int, threshold int) int {
+	pfs := pfSum(mat)
+	w, h := len(pfs[0]), len(pfs)
+	maxAllowed := min(w, h)
+
+	l, r := 0, maxAllowed+1
+	for l+1 < r {
+		m := (l + r) / 2
+		if hasSquare(pfs, m, threshold) {
+			l = m
+		} else {
+			r = m
+		}
+	}
+	return l
+}
+
+var _ = maxSideLength